They went about it well, taking some of the basic plot elements from the game, but creating an original story from it that doesn't try to follow the game too closely (because even though the game had a really cool story, it wouldn't translate as well to film.) I liked the pacing of the film, and it was definitely of the sort that if you didn't have knowledge of the franchise, you wouldn't feel like you were watching a video game movie. There were only a small handful of characters in the film who had counterparts in the game, and the original characters who were added in all felt like natural fits in that world.
I really liked the action scenes in the movie, and the parkour was awesome (I'm a sucker for parkour in movies, though.) I had a minor geek moment during the city invasion at the beginning as Dastan surveyed the area, & they swung the camera in the same way you would when scouting out jumps in the game. It was a nice nod to the gamers that didn't detract at all from the experience.
While I was watching the movie, the one thing that kept bugging me was trying to figure out why I recognized the actor who played Prince Tus. It was driving me nuts, because he looked & sounded insanely familiar. Then once the credits rolled, I saw it was Richard Coyle from the British version of Coupling (which I love), and it made me happy that he's finally landed a major role in Hollywood. "Richard Coyle: Great actor, crap with doors"