For a game that offered no in depth customization for your vehicles, GRID rises up and comes out as one of the best.
It was the first racing game to offer the "Flashback" system. A long overdue feature I might add, but GRID got at it first, and you can see newer games now coming out with something similar. Forza 3 for example is having the "Rewind" system, which in all reality, is the same thing.
GRID also emphasized the severity of crashes. The damage engine that Codemasters used was amazing. They even went so far as to put in a Demolition Derby style race to showcase this engine.
The racing engine itself was put together masterfully. The reason that they didn't offer the tune-up feature was because they didn't have to. Cars that should corner well did, and vice-versa. The online racing is intense and tight, with a few lag issues, but nothing major.
Bottom line is that GRID is a racing game that no racing fan should be without. If you are a true racing fan, you owe it to yourself to at least try this game. Trust me on this, you won't regret it.