Don't let yourself fool by the positive reviews, this game is the same garbage as many other license games, on top of that its an awfully frustrating experience.
First of there would be the story or better lack there of. The game really doesn't connect to the Simpsons at all, instead you simply have a GTA clone featuring Simpson character. All your missions resolve around collecting stuff or driving trough checkpoints on a timelimit, so don't expect any puzzle solving or dialog that would actually construct a story or make the game world feel alive. Then there are the graphics that are somewhat acceptable, but suffer quite a bit from tearing artefacts, a few framerate drops when your car casts smoke and lack cell shading, which makes it look very different from the show. Proper facial animation are also lacking.
The voice acting itself is ok, but when the dialog itself is pretty uninteresting and boring that doesn't really help much.
In the end what puts this game down the most however is the missions design. Basically everything resolve around collecting things on a time limit, an at times extremely strict time limit. So you spend very little time having fun and instead most of your time learning the track to get a perfect run done, as basically every little mistake causes you to restart a mission, especially in the later levels. The chances of making a mission on the first try are slim to none.
Overall the game is just very frustrating and very little fun, while making little good use of the license material.