I have to agree that overall, it was a very good movie.
I saw it again with a friend, and we spent out time analyzing the movie. We both agreed that the way they used Focusing (like with a typical movie) was disappointing, as the 3D could be used to fill in the rest of that area. We also agreed that the storyline was alright, but there were holes in it big enough to drive a truck through (or one of those hammerhead things). For instance, what exactly was the atmosphere? They just needed masks with air purifiers, not tanks. So it obviously had oxygen. Same goes for the fire. It would not be like that considering the different elements in the air, either burn more, less, different colours, etc.
Also, the 3D could have been used to fill in the foreground more, as my friend mentioned. Instead, they kept it confined within the screen, though they did have fairly good depth.
So besides the plot seriously lacking, and the 3D and filming needing to be used more.... It was still a good movie. The plot was not original, but its hard to be truly original these days.