Best: Saints Row: The Third. Started it expecting to be underwhelmed, finished it thinking I could go back and play it a few times more at least.
Worst: Call of Duty: Modern Warfare 3. Why I expected it to be any different to the previous games (no I haven't bought them but I've tried them each for about an hour) I have no idea. Glad I didn't pay full release price for it.
Biggest Disappointment: Test Drive Unlimited 2. All the original hype and potential turned into a big let down. Boring (easy) races, rubbish physics, still loads of bugs, hardly any support after it's release in terms of patches and no downloadable content which was promised before release. It had the power to be something great, but it turned out to be a lot worse than it's predecessor. Too much focus on the naff social aspects instead of the core driving which is what everyone wanted it for.