Well, one point in my first post still stands: it was the best Marvel movie I've ever seen.
I actually really liked it. It pains me because I couldn't find much to bitch about. Chris Pratt was great, like I suspected he would be, and Rocket was awesome.
The biggest issue, like others have stated, was the villain and the "chase the macguffin" plot (although this was lampshaded a few times, which I appreciated). The movie was so much fun that it was hard to care about the conventional storyline and shallow villain. I would have liked more Thanos screentime, but whatever. Knowhere was also a really cool setting, something you'd see out of Doctor Who or something.
I haven't seen Avengers or many Marvel movies recently, but isn't an infinity stone the driving force behind a few different recent Marvel movies?