Guardians of the Galaxy is the first of the Marvel movies that I'm coming into with, basically, no background knowledge of. Which is not to say that I don't know the general layout of what's going on, but the Guardians that I used to read back in the 90s
is not the same Guardians that exists today. And the characters that I am familiar with, like Drax, are not quite the same (since Drax is not functioning as a herald of Galactus in this Marvel Universe (because, you know, Galactus is being held captive over at Fox Studios (which is actually pretty scary when you think about it))).
That said, stemming from what Marvel has done with their previous movies, this one picks up the thread and weaves it in seamlessly. But in a completely different way. [And I just want to point out that this is the kind of movie that DC's Green Lantern should have been but failed utterly to be.] So, yes, this is a departure from the previous super hero Marvel films, but it's not a departure in quality. Though, to be fair, there will be people that won't be able to accept characters like Rocket and Groot even though they were brilliant. [My kids loved Rocket even more than Groot, which is saying a lot.]
What the movie does:
1. Introduces the idea of the Celestials.
2. Gives us a clear view of the wider Marvel Universe
3. Applies the term "Infinity Stone" to the infinity stones for the first time.
4. Gives us a better idea of who and what Thanos is.
Guardians does a good job of sprinkling in humor without ever going over the top with it. It doesn't over balance the action or the seriousness of the situation. And it's spread evenly across the characters so that it's not just a bunch of one liners from Rocket or anything like that. Drax has some great, humorous moments even though he is nothing but serious throughout the film. It's very well done.
The acting is spectacular. Chris Pratt, whom I've been a fan of for quite a while, was amazing and the right pick for Peter Quill. Bradley Cooper was surprisingly good as the voice of Rocket. Surprising in that I couldn't even tell it was Cooper doing the voice. Neither could my wife, which is saying a lot, because she always knows the voices; it's a talent of hers. Cooper gave authenticity to completely realistic looking CGI raccoon. Karen Gillan also stood out as Nebula. It was a complete departure from her role as Amy in Doctor Who.
The short of it is that, really, I was ready to see it again as soon as we walked out of the theater. My kids would agree with that. It was a lot of fun. Most similar to Iron Man in tone because of the humor but handled in a way that kept it from becoming campy. I think I'd say it's like an awesome roller coaster ride, the kind where, as soon as you get off, you want to go back around and get back in line.