It's the oddest film so far in MCU's Phase Two: it doesn't have any clear connection to any of the other films outside of the Collector, who was in the after-credits scene for an earlier Marvel film. Plus, there are a lot of comic continuity heavy references - not too many to confuse newbies, but it definitely keeps comic books readers in a good mood.
It wasn't the greatest Marvel film to date - I thought Karen Gillan's turn as a super-villain was wasted, I wanted more Gamora, and my mom wants to know who Star Lord's dad is (I know but ssssshhh comics) - but it was loud, colorful, fast-paced, and fun to watch. I described it to my sister as Marvel meets Space Dandy with a better soundtrack, and I stand by that comparison.
And yes, you must stay until the end of the credits. You don't want to miss the Easter egg Marvel stuck on this one! And, of course, keep an eye out for an in-film cameo from Stan Lee, but that's to be expected at this point.
So if you're not yet totally talked out about GOTG, drop your feelings in the comment section!