So, I've decided to set this down is metaphorical stone, to act as a truthful, hopefully unbiased comparison of the three most recent Elder Scrolls games in order to help people such as myself to learn more about the games before trying them and to know key difference and similarities between them.
My short analysis will focus on five key areas (which may overlap in places): World - Environment, Scale and Quality NPCs and Creatures - Enemies and NPC interactions/personality Quests - Main Quests, Guilds and Side Quests Immersion - Impact on World, Depth, Role-playing potential and Realism Misc - Magic, Skills, Accessibility and Items
I will do this by area of analysis, not by game, so that people interested in a specific area can compare more easily.
So. here goes:
World
Morrowind - Definitely the most alien and unique world. Full of towering mushrooms, volcanic badlands, rolling plains and fair sized cities. Cities of a decent size but sometimes (excluding Vivec) feel slightly too small. World feels unique in different regions, Ashlands of the north feel a world away from the swamps of the South. Dungeons similar enough to notice but unique enough to enjoy. There is a definite sense of wonder and urge to explore.
Oblivion - A much more generic fantasy setting (Castles, greenery etc) World not as alien or varied as Morrowind with most of the map being either green forest of green/yellow plains. Cities feel large and believable and are numerous. Many more towns and villages than Morrowind or Skyrim. Dungeons are ok, but definitely feel similar after only a few. Especially true with the fort ruins of the game. Sense of wonder and urge to explore not as strong. (That may be personal, as Cyrodiil looks alot like Britain, my home)
Skyrim - World is more mysterious than Oblivion but not Morrowind. Cites are smaller than expected but compensate in other areas. Snow areas aren't particularly interesting but other areas like the marshes around Morthal and volcanic springs of Eastmarch make the world feel satisfyingly varied. Dungeons feel much more unique than Oblivion's or Morrwoind's, especially since many more dungeon designers were used than in previous games. World invites exploration and many places genuinely astonish you.
NPCs and Creatures
Morrowind - Creatures are weird and wonderful, but human enemies are bland and boring. Much more fauna variety than other games. There are many more NPCs who can discuss a wide range of topics and conversation pays off, but almost all NPCs provide identical responses and very few NPCs in the world have any personality whatsoever. Cliff racers make me want to tear my face off.
Oblivion - Enemies tend to repeat more often but they are still reasonably interesting. More NPCs have character and personality but a very large number still feel like simple filler material. Fewer topic to discuss, with fewer NPCs willing to discuss them, but dialogue changes between NPCs much more often than in Morrowind.
Skyrim - Enemies have a good balance between variety and interest. Dragons are cool to behold, but fights with them become somewhat repetitive after a few hours. NPCs have fewer topics to discuss but almost every named NPC has a personality, allegiance or story to discover. Dialogue is quality over quantity.
Quests
Morrowind - Main quest is enthralling and of the perfect length (long enough to be invested, not long enough to get bored). Uniting tribes and houses feels rewarding and fun. DLC main quests often start off slowly and improve later on, especially Tribunal. Guilds are more realistic than other games. Guild quests consist of normal jobs, not a story, in which you ascend ranks by completing real jobs, much more believable and rewarding. There are more than double the number of guilds, though joining one can lock out another. Side quests are strong, with a wide variety of objectives and styles.
Oblivion - Main quest tedious and boring. Knights of the Nine feels like a typical 'knight in shining armour' ordeal with an Elder Scrolls twist, fun nonetheless. Shivering Isles is a wonderfully mad and varied place, but quests are still mostly fetch this or fetch that, but interesting environment and enemies make up for it. Guild quests blend good story and uniqueness with sense of progression and realism - arguably best guilds in the series. Side quests are a mixed bag, some excellent (the painting one especially) and others horrifically boring.
Skyrim - Main Quest reasonably fun and rewarding (Dragon shouts FTW) and does'nt last too long. Dawnguard is ok, but not of perticular note. Dragonborn has interesting themes but main story is awfully short. Guild quests are fun but are very short, you beocme leader very easily and any play style completes and story (Heavy armoured axe wielder as Archmage). Civil war is fun for battles and conflict but not very deep or unique. Side quests flow naturally and come in a wide variety. Radient quests add infinite jobs in over a dozen differnet themes (Thieving, assasination, animal controls etc) but get repititive after a while.
Immersion
Morrowind - Beleivable and changeable world. Joining one faction can lock off others (Joining one Great House means you can't join another. Books and dialogue are expansive and add huge depth and realism. NPCs can hate or love you depending on your actions. Who you kill or spare can drastically change a faction or person's view of you. Role-playing is somewhat restricted to adventurers and guild members. Much more realistic with consequences, limitations and rewards for everything you do.
Oblivion - NPCs treat you slightly differently depending on their opinion of you, but not on Morrowind's scale. Faction membership has little impact on the world aside from changing Infamy (which doesn't really do much). However, completing main quest makes oyu a hero to the people and they will treat you accordingly. Role-playing expands to allow a wider range of choices and themes.
Skyrim - Few consequences or restriction are placed on the player. The only times joining one faction alienates another is Imperial vs Stormcloak (which are very similar anyway) and Blades vs Greybeards (which can be completely ignored). NPCs will treat you slightly differently under certain circumstances but these are usually the result of a direct quest. Aside from the odd guard, no one cares that you saved the world from Alduin and people still talk down to you. Role play is superior with many more things like farming, mining, cooking, smithing and wood chopping allowing more choice for role-play builds.
Misc
Morrowind - Game is very much old-school, can scare off the more 'casual gamer'. More skills but you never feel truly unique as a character. Magic is varied and useful with a huge variety of non-combat and combat spells. Many more armour slots allow greater character customisation. Wider variety of weapon types is also available. Combat is stats based and awkward. Combat starts off hard but becomes incredibly easy later on. Stealth almost non-existant and point-blank misses are frustrating.
Oblivion - Game much more streamlined than Morrowind but looses it's charm. Uses quest markers rather than Morrowind's directions. Much more "pick up and enjoy" than Morrowind's "pick up and get killed by rat". Magic is not a viable option without a staff or strong armour (I've been informed that this isn't that case at higher levels, so ignore my ramblings). Spells are decent and spell-crafting just as good if not better than Morrowind. Enemies level with you and get the best weapons and armour, making levelling up pointless. Stealth is slightly better but bows are underpowered. Combat is based on physical accuracy not stats making it much more fun.
Skyrim - Even more smooth than Oblivion, using quest markers is still a controversial topic. Can be picked up and played like Oblivion but getting the most out of the game comes from true investment. Magic is much more viable and believable but spell-crafting no longer available. Dragon shouts are a brilliant addition and are well balanced. Levelling is based on perks allowing characters to have abilities and specialisations rather than Morrowind and Oblivions linear "more power!!!!!!" style of skills. Enemies level well, with weaker ones still appearing at lower levels. Combat improved and refined on Oblivion.
That was a brief summary of the main areas of importance but there's still so much more. Now, there'll be many asking "Well, that's well and good, but which is the best?!". Truthfully, it depends what you want.
Morrowind is much more hardcore and challenging and best for players already seasoned in the Elder Scrolls. Consequences, limitations and reputation aren't the best things for the light-hearted. But, for those who get past the 12 year old graphics and long-retired RPG mechanics, you will find an amazing game. I only started playing about a month ago but is is undoubtedly among my top 10 games ever. It's just that good. In my opinion, Morrowind is the perfect example of the old favourite: "Good graphics don't make good games".
Oblivion is somewhere in the middle and an acceptable starting point for series newbies. Whilst it is rough around the edges, it is still a great game. It's tone is much more comical and many quests (and of course the Shivering Isles) reflect its somewhat wacky nature. In my opinion, Oblivion is the weakest of the three, but still a great game. For someone like me, who lives in a country built on knights, castles and rolling green plains, Oblivion doesn't feel like an adventure on the scale of Skyrim or Morrowind. But, that's just me. For other people, Oblivion still holds some of the most enjoyable and beloved quests and locales in modern RPG history.
Finally, Skyrim. The most recent of the series. I'll say now that it is, still, my all time favourite game. But I'll try to keep the bias of a 1000 hours of game-time out of the veridct. Whilst not as hardcore as Morrowind or even Oblivion, Skyrim is still an excellent game. It does get bashed alot by long-term Elder Scrolls fans for being "dumbed down" but I simply don't agree and it's still as vast, fun and enjoyable as any of its predecessors. I'd recommend it as a starting point for newbies to the Elder Scrolls but I'd highly reccommend trying the others later on once you're used to it.
So, there we are. My attempt at a summary along the lines of what I spent ages looking for. Just to clarify, I love all of these games. The past month has been one of the most enjoyable of my gaming life and I'd recommend Morrowind, Oblivion and Skyrim to everyone, newbies and veterans alike.
If anyone would like me to expand further on these points then say so, I'd gladly do so in comments.
Can I also give a special mention to r/Morrowind for all the help, answers and responses from my posts when I started and also for giving me tips and help throughout my adventure. Azura bless you, Outlanders.
Also, to r/Oblivion who helped me kick my meta-gaming habits of main quest-DLC-guilds and allowed me to truly appreciate the brilliance of Oblivion. In a way, you're kindness has made me somewhat of an Adoring Fan...
Morrowind is hands down the best video game I have ever played and honestly I dont think a better game will ever come out, unless sometime in the future virtual reality morrowind is released. The sense of awe I experiences when I first saw this game was unbelievable. I had not seen a game like it at the time. The game was an enormous playground that was ready to be explored to the nth degree. You never knew what cazy armor or weapons you would find on your next journey through a dungeon. Skyrim basically gave you all the daedric artifacts, there was no challenge at all. The sense of satisfaction when completing a daedric quest without any help that was just amazing. I also loved how the journal worked in morrowind. I liked how vague it was and it actually made you think about where you had to go and what to do. Like the quest where it said go to the point between two hills in the north when the sun is setting. That could be almost anywhere and finally finding it was amazing. It didnt put an arrow on the map that told you exactly where to go. I hate all the handholding that oblivion and skyrim did. Exploring was natural to the world of morrowind and there was no instant travel from any location which forced you to walk places and stumble across dungeons with potentially the best weapon in the game. The story was also very epic. Becoming the Nereverine and Hortator was really awsome and I actually felt like an important person. Some of the quests pissed me off like the one where you had to dress the chick up and escort her. All in all though the story was very good and the DLC or whatever it was called back then made it even better. The only bad thing I can think of about this game is the graphics which now are horrendous, but hey it came out forever ago and at the time they were pretty good. I am sad that most people in future generations will never get to experience the masterpiece that is morrowind.
I understand that there are different genres of game but quite frankly I dont care. This game is just way too good and nothing even comes close.