I also saw Ender's Game on the opening weekend and I enjoyed it quite a bit. Solid performances by all of the actors, the themes were well expressed, the tension and the emotions were spot on. On the downside, there was a lot of stuff from the book that I missed, particularly regarding Valentine and Peter (not the political stuff, but their relationship with Ender).
Actually, I felt the pacing was a bit too fast, but i totally understand there is only so much you can do given the time constaints; and it is a movie, not a book.
All in all I thought it was an impressive adaptation of the story, better than what I was suspecting given the current movie industry, and the economy of time and content. In my opinion, you couldn't really have asked for a better Ender's Game movie.
And it was 20 times better than the Hunger Games adaptation.