I enjoyed the movie. And like a lot of other people I didn't have any previous exposure to the GotG comic. But the movie stood well on it's own and the characters were interesting. I may go back and see it again.
Seeing some of the big cosmic players in the Marvel Universe on screen like this was great. Without getting into spoiler details there were so many civilizations and individuals that got touched upon: Thanos, Ronan the Accuser, the Kree, Xandar and the Nova Corps, the Celestials, the Infinity Stones and the Collector. WHOA. That's a lot of Marvel cosmic territory to cover, but it got done without shoe-horning.
I really liked getting to see the Collector's museum. Obviously, there were the two characters that were seen in the post credits scene. But in the initial scenes I also noticed some other beings in the collection that we'd seen in previous movies, like a Chitauri as well as a Dark Elf.
And another thing that I noticed? On one of the ships there seemed to be some glyphs that resembled something we saw on television. Hmmm...