Personally I liked it. One of the better (if the not the best) movie I have seen at the theater this year. I am not a comic book fan, and in general I enjoy movies because I view them as what they are: visual and audial entertainment. In this movie I laughed a lot, there was almost always something going on in the background that was funny or at least entertaining, and the characters actually had some depth, at least enough for me to care about them (ie like or dislike them).
Compared to movies like Lucy and TMNT, this one deserved a friggin Oscar..
Like I said in another thread about this, if I want a deep story and characters I can visualize as real people, I read a book. The moment you expect a book or graphic novel (or even comic book) to be better as a movie is the moment you need to go watch Howard the Duck or Battlefield Earth. And after you realize you can never get those 2-3 hours of your life back, go back to reading.
For a MOVIE, Guardians was great.