The general consenus amongst fans is that this Potter movie while still good, is a major let down. Things people really wanted to see were left out. Like the big battle at the end. Its a good movie, but not the best in the series as many reviewers claimed. For many people this was just a middle movie. Everyone wants to see the end of the series, so those movies are going to be huge.
G-force being in 3D helped its box office total Im sure. It is a good movie though and I hope it catches on with the kids.