I think I must be the only one who wasn't over the moon for GOTG. I liked it plenty, but man did it have a lot of writing problems.
Ronan was a horribly written character. This is a real shame because he would have been awesome if they just kept him like the comics. In the movie I had no idea what his motivation was beyond generic bad guy revenge stuff. The dialogue between Thanos and anyone was awful. The plot, in general was really weak. And, sadly, Gamora was terribly cast. And man, did they ruin Xandar and the Nova Corps.
That said, they really did a great job with Star Lord, Rocket, Groot and Drax. And it was very fun and very well directed.
The sequel has a lot of things going for it and I'm hoping it's handled better. Of course if it's as good as the first one, it looks like everyone but me will be perfectly pleased so it's a win-win for them.