If mud were blood, this game would be rated MA.
The game took me a good 15-20 hours to complete, spread over the course of a good 4 or 5 months. (granted for 3 - 4 of those months I was playing World of Warcraft). Each level getting increasingly difficult, However, there are only a hand full of "extra" hard races in this game, peppered through various difficulty levels. I found the majority of the big rig races to be some of the most difficult in the game.
On average, the game is relatively easy once you learn the tracks. I was rather disappointed to discover that there is generally one "main drag" path through every course that will generally always (regardless of what vehicle you're in) net you a first place spot. This isn't true for ALL the tracks mind you, but a good majority of them. Another thing that kinda let me down was the extremely non-climactic end of the game. There is virtually no replay value other than online or the new time trial mode. I was kinda hoping for some sweet unlockables or whatnot, but nope. It looks like we will just have to wait for evolution to release some new tracks and models for us.
Aside from those things, This is all together a very decent racing game, complete with high-energy boosting, and amazing crash sequences. This game is by far no slouch when it comes to actual gameplay.
If you're looking for a game to sit down with, and have a good challenge, or just a game to show off your new HDTV, then this is a good choice!
But if you're looking for a game to play for years to come, you might look for Motorstorm 2, which is sure to have split screen.