If you don't play multiplayer then you haven't played the game.
The graphics this game has are amazing. If you have the free version I am willing to say that this is the best looking free game out there. Game play is addicting, online makes you come back for more as every second another track is being released by someone out there in the community. Apart from what veterans call the loop bug and some other very rare occurrences, the game plays flawlessly. Cars are fully customizable assuming you have the know how to do it. You can model you're own car and import it into Trackmania or you can take a less advanced route and use Photoshop to skin you're car or a car you downloaded.
There really is nothing to not like about this game especially considering you can get it for free since the only really good part about it is multiplayer. It's called Trackmania Nations.