Stargate (Roland Emmerich, 1994)
Stargate SG-1 (Brad Wright and Jonathan Glassner, 1997-2007)
Stargate: The Ark of Truth (Robert C. Cooper, 2008)
Stargate: Continuum (Martin Wood, 2008)
These three films and one TV series chronicle the story of an interplanetary teleportation device, known as the stargate, through its discovery on Earth and the ensuing exploration and militarisation by the US Air Force. There's a lot of variance in plot, characters and quality of screenwriting throughout the 15-year story, so I'll go through them one by one.
Stargate is a passable but altogether underwhelming introduction to the universe. As enjoyable as it is for the mythological references that would be gradually phased out through SG-1, the characters are very cliche and predictable, and it follows the done-to-death frame narrative of "introduction / complication / resolution" we learnt to write in school. Not a bad movie, but it stops short of being a good one.
SG-1 starts out picking up the pieces from the film, and for the first couple of seasons fails to amount to anything greater. Once again, the main appeal of the early seasons is their focus on mythology, with the dominant alien races (in particular, the Goa'uld and the Asgard) having taken on the role of gods at some point in Earth's history. Throughout SG-1, the fun episodes are the only ones which manage to be consistently strong, possibly due to not taking themselves too seriously. "1969" is a good early example of such.
Things start to pick up towards the end of season 2, and the various story arcs involving the Goa'uld, the Tok'ra, the Asgard, the replicators and the Ancients make up the meat of seasons 3 through 7. Those five seasons are SG-1's best, in my opinion, finishing in a cliffhanger reminiscent of The Empire Strikes Back, as one of the characters is frozen in stasis under less-than-ideal circumstances. The classic SG-1 lineup of O'Neill, Jackson, Carter and Teal'c remains the best one to date, although Jonas Quinn made a nice addition in season 6.
Things started to fall apart as the central characters left the show, and none of their replacements ever quite filled the shoes of their predecessors. Season 8 was saved from total disaster by a few well-written episodes (the finale in particular), and the fact that O'Neill was still involved, even if to a lesser degree. It was also the last season with the Goa'uld as the dominant enemy; who, for whatever faults they may possess, felt like a relatable and tangible threat, without invoking too much suspension of disbelief.
Season 9 was the worst of the run. The new leader, Mitchell, failed in every way to live up to either O'Neill or Carter's leadership abilities, and felt like a cheap substitute for O'Neill's happy-go-lucky humour. Carter was absent for the first half of the season, and while I like Vala as a character, her constant antagonism of Daniel Jackson got old fast. Couple that with a confused jumble of story arcs involving the newly-introduced Ori shitlords, the last of the Goa'uld and the newly-formed free Jaffa nation, and the season really doesn't go anywhere. It ends in another mythological reference, this time relating an ancient battle against the Ori to Merlin and King Arthur, but by now it just feels like a token effort.
Season 10 was made slightly better by a more consistent focus on the Ori as the main threat, although they're still a much less well-developed enemy than the Goa'uld ever were. The finale, "Unending", was the highlight of the last two seasons, partly due to disregarding established story arcs and focusing on creating a well-written standalone episode, as many season finales before it did. At least it ended on a high note.
The two follow-up films, The Ark of Truth and Continuum, couldn't be more different from each other. Ark concludes the Ori story arc from seasons 9 and 10. As if that weren't bad enough, they introduce a brand new civilian government character whose sole purpose is to fuck up all of the military's plans by re-introducing replicators (an enemy previously defeated once and for all) without good reason or clear motive. The replicators then attack that guy (who is so unmemorable I've forgotten his name) to create a replicator/human hybrid who fights hand-to-hand with Mitchell. No doubt it was intended to come across as impressive or scary, but it just looked ridiculous.
Continuum, on the other hand, concluded the Goa'uld plot by portraying the death of the final Goa'uld system lord, Ba'al. While his execution takes only minutes, the majority of the film is taken up by a deviation in the timeline, whereby Ba'al tries to undo all of the accomplishments of SG-1 by going back in time and preventing them from ever discovering the stargate in the first place. While I am a sucker for time travel, I also genuinely think this is better written than The Ark of Truth, not to mention that O'Neill makes a comeback (which is always worthwhile).
The SG-1 narrative is among the most inconsistent sci-fi I've watched. Overall, I liked it a lot, but it had a lot of weak spots where not much interesting happens for many episodes at a time. All things considered, I'm glad I watched it, but I probably wouldn't watch it all the way through again; I'd pick the good bits (seasons 3-7 of SG-1 and Continuum, mainly) and skip the rest.