I love the original Thief and Thief 2 is a close second. The graphics are largely similar to the first game (with a few enhancements) but this series was never about the graphics! In Thief 2, the gameplay focuses a bit more on sneaking and thieving (unlike the latter levels of the original) and gives players another spectacular time doing so. The story of this game takes the series in the opposite direction. The first game focused on an imbalance in the world, namely nature and the pagans threatening to shift that balance with the return of the trickster. Thief 2 also has an imbalance, but this time in the form of science and technology threatening the balance. As always, the keepers are present in the shadows trying to guid Garret in an attempt to restore order and balance. This game is worth it. Trust me.
Thief is one of the best games that has ever been made. I can still remember when I first bought the game (it used to come in those weird triangle boxes that Eidos shipped their games in). It was like no other game I had ever played. The game rewards you for being stealthy and taking your time. I can't even count how many times I had to replay each level before being able to move on. This game was revolutionary for the time, and in many ways, is still way beyond any stealth game that has come since. The GOLD version of the game adds even more levels to the fun. Seriously, buy this game, you will not be disappointed.