I don't normally do two movie reviews in the same week, but, then again, we don't usually go out and see two new movies in a week either.
This is the sort of movie that is so much fun, you don't notice, or really even care, that large parts of it make no sense. So I'm not even going to bring that stuff up.
The movie is pretty much completely divorced from the main run of Marvel movies. The only connections are a character known only as The Collector and Thanos. Both were mentioned in end-of-credit clips from other Marvel movies. The Collector (last seen in "Thor: The Dark World") doesn't have a major roll here, but Thanos ("The Avengers") does. My daughter, who is much more hip to the Marvel Universe than I can ever hope to be, is certain that the next Guardians movie will feature them and the Avengers teaming up against Thanos. I think I've also seen that on io9.com.
In addition to great effects and "an end of the universe" plot, the movie is also funny. There are a lot of through away lines and even the occasional slapstick to keep things lighter than the plot would suggest.
I'm still trying to figure out why they got Vin Diesel to voice the Groot character. He only has one line, "I am Groot" which he says over and over.
Be sure to stay until the end of the credits or you miss a cameo appearance of one of the greatest Marvel characters ever.