I liked it, but didn't love it. I can't really explain why I left a little unsatisfied (though the awful post-credits sequence probably helped), the humour was good (though maybe too frequent) and the action was exciting (if a little too screen-filled and overwhelming). The dialogue was superb but the plot wasn't very good. Needlessly complicated and missing key beats. Also, it felt like a smashing together of ideas seen elsewhere - Star Wars, Serenity, Chronicles of Riddick and Spaceballs being the ones that to come mind most readily.
I couldn't help but feel that I was missing out on a lot of the nuance of the setting, not having read anything about these particular characters. To be honest, at about 20 minutes or so, I was completely lost as to who was who and how all these planets related to each other. Whilst you can get away with more when you set your movie on Earth, you don't really have the luxury of skipping a prologue (LOTR) or some sort of monologue narration (Serenity) when your entire galaxy is a mess of new terms, planets, races and organisations.
And here is another big movie where the climax involves thousands of innocents dying and the heroes failing to protect them. Half the city was destroyed by Ronan's ship and yet there was no attempt to divert it or even acknowledge that it was going to crash on the city.
Maybe that's it, I don't think the ending battle was put together well at all. Seemingly significant actions lack context to make them significant (e.g. The Pointless Net of Ships), actions are dicated but aren't seen to be occuring (people aren't evacuated), the goodies lack powerful defenses or capital ships or don't use them, duels occur but don't resolve, an at-this-point virtually all-powerful villain stands around/or hides behind a wall, there's no plan to actually deal with Ronan etc.
To my mind, the film needed to establish the Nova corps better and show them to be powerful force that are clearly superior to Ronan's forces. I didn't buy that Ronan couldn't wipe them out without the stone or Thanos' help (which is the entire driving force of the story), as just his ship and nondescript army practically curb stomp a reinforced corps. The film needed an early scene where Ronan is forced to retreat from the Nova guys, making his search for the stone his motivation and placing his eventual acquisition of it into the context of major shift in the balance of power. Yet instead, Ronan goes from place to place without any fear or Nova corps interference. Why does he need Thanos' help again?
Lastly, it doesn't bode well for the uber-villain that you're building up as a key player in future movies when you have him do literally nothing and drop out of your story when a formerly cowed minion gives him the middle finger.
