Just saw it tonight. Thoroughly enjoyed it.
Theatre here had a 10-minute break after about an hour. I felt the two "halves" were very different. First half had a lot of character development, dialogue and some witty lines and jokes here and there (If you're a Joss Whedon fan, you know what to expect). The best part of the movie in my opinion. The second half had a lot more action. It definitely still had some great moments but overall I thought it had more weak points as well.
All in all, it's not an absolute cinematic masterpiece, but if you like the idea
of a superhero movie, if you like the avengers of if you like Joss Whedon, this movie definitely delivers.
I hear Whedon really pulled off the group dynamics (Movie Bob if you care), I guess this doesn't surprise me, he fucking nailed Firefly group dynamics.