Even though I didn't have a whole lot riding on this particular movie, I did feel that the one thing they'd have to get right, or the whole thing would fall apart, is Rocket Raccoon. (And as has been noted before, it is kinda sad that he made it to the big screen before Wonder Woman.) Obviously, he's all CGI, but he's an important member of the team. Sure, Groot, the living tree, is an important member as well, but he can't hold a conversation the way Rocket can. I thought it was an interesting choice to get Bradley Cooper to do his voice, as he's not exactly an obvious pick. Had they done this movie in the 1990s, they probably would have gotten Robin Williams or Jim Carrey to do it and play it strictly for goofy laughs.
Do they get him right? Yes. They totally nailed it. Honestly, I wouldn't have guessed that it was Cooper doing the role - who knew that he had a talent for voices? And yes, he's a humorous character, but the humor comes organically out of the fact that he's basically a talking raccoon, yet he has no idea what a raccoon is. Also, most of his funny lines would have been funny if any character said it. In other words, it's not a bunch of lame raccoon puns.
Honestly, I thought that Peter Quill, also known as Starlord, was more interesting in the movie than he's ever been in the comics that I've read. He seems kind of a blank slate in those, but he's given some real heart and motivation in this movie. I can't say that there's a character in this film that doesn't work.
The special effects really show how far things have gone. Yes, it's heavy with CGI, but I found myself immersed in the world that was created. Also, it reminded me of how crappy Green Lantern was, or more specifically, the special effects from that movie. Guardians shows that you can have other worlds that aren't dark and blurry, as the main planet that they have to save is bright and vibrant. I'm not sure how much of it was models and miniatures, but I completely bought into it.
My only complaint is that it starts to fizzle at the end. I think that the best example of a movie's end fight scene being more satisfying than exhausting was in The Avengers. With this, it felt like it was going on a bit too long in an effort to end with as big of a spectacle as possible. Still, overall this was a pretty strong film, and I look forward to seeing these characters not only return in their own sequel (which has already been greenlit) but interact with the characters from the other Marvel Studios movies.
Oh, and it's killing me to not discuss the post-credits sequence. For those of you who saw it, let me just say that as far as what it introduced is concerned, I was okay with it being there. Hopefully, I think that this should not be a hint of what's to come but the end of that particular concept.