Test Drive Unlimited 2. Played the hell out of the first one and bought the second on release day. They added things that fans wanted, like weather effects and a day/night cycle, but then completely gimped the physics and force feedback, and removed a lot of the graphics/setup options that were in the first one. The physics and ffb are the very soul of a driving game, and if that's not satisfying, then the game will get dull quickly. And I really hate it when I can't turn off frikken motion blurring.
Here's a tip, Atari/Eden - when you make a sequel, don't REMOVE features that were in the first one.
Need For Speed Hot Pursuit was pretty disappointing as well, after everyone kept saying how it was a return to form for the NFS series. It was little more than a reskinned Burnout, imo. It didn't even have the option to select manual gears ferchrisakes. I'm pretty sure the people at Criterion have never actually driven a car.
PC version for both.