What are your favourite computer games/board games and why?

I've been a PC gamer mostly, until just recently, and into a lot of different types of games, everything from Company of Heroes to World of Warcraft. Each game usually has a particular 'something' to offer that pulls me in, but it can vary greatly from game to game and genre to genre. Overall, a truly great game presents a sense of immersion from all aspect of its development. As cheesy as this may sound, I was actually most impressed with Fallout 3 for exceeding my expectations of the series. In fact I just played the PITT last night and it was awesome!