I finally saw it today, SPOILERS BELOW but I suspect anyone who cares has seen it by now...
It was good. The second half was a lot better than the first half, so that's good in a way because it finishes strong. What it did very well was the emotional scenes. Yondu's death was very sad and Michael Rooker did a great job throughout giving the character depth. The funeral with the Cat Stevens song and Sylvester Stallone and everyone, all good stuff. Gamora and Nebula hugging? Beautiful. All their scenes together were so good that I'd love to see a spin-off where they go off together to save other girls from Thanos. Drax talking about his wife and child, Rocket crying...like I said all the emotional stuff realy worked.
Ego was a good villain. I mean, he did just end up having another "end all life in the galaxy" plan but it was a much better excuted plan than the one in Thor: The Dark World. His planet looked cool (love the shot of his face on it.) Mantis was a fun cute new character. I liked the gold people and their video game style drone ships ("you suck, Zylak!") A lot of the humour was very good. Drax got most of the funniest lines and I always enjoy seeing Dave Bautista do so well.
But that brings me to the negatives: some of the humour didn't really work as well as the first? It all seemed, epsecially in the first hour, dialed up to eleven. At one point Nebula said "all you do is shout at each other" and I was thinking "yeah, I wish they'd stop that" because there was a bit too much of it, especially from Rocket. Not every joke has to be shouted! When Peter and Rocket were aruging at the beginning it just made them both seem like assholes rather than being endearing. And there was one bit there Nebula told her really tragic backstory about her abusive father than they instantly undercut it with humour. It would have been a lot better without the undercutting it with humour part. Some of the jokes seemed to go on too long and then after a character (Drax or Rocket) would laugh for ages just so you knew what the jokes was. While Ego was a good villain I'm not sure why they took so long to reveal his evil ways. I mean, no one was going to believe that someone angry that her batteries were stolen was the main villain of the movie.
I liked the end credits and how Jeff Goldblum randomly appeared dancing in a bubble because who's going to stop him.
So yeah, it's definitely a very good fun Marvel movie but I wouldn't put it in my top five vey good fun Marvel movies just because there was stuff that didn't work for me.