Half-Life 2

Just finished Half-Life 2 (after about 18-20 hours spent over the last 5 days) on it. This — seeing my currently available spare time — is quite an achievement and shows the very high quality of the game. It is relatively hardware-friendly (i.e. it was fun to play on my machine — in contrast to the CPU-hog Doom 3).
I got the game over steam (via an ATI-coupon that I upgraded to “Silver” for $10) and had absolutely no problem activating it whatsoever; one advantage is that I can install the game on my laptop and on my home machine at the same time.
The graphics are amazing, although a good deal is independent of technical merit and is simply very good art direction; nevertheless there are some very neat effects in there such as distortion or good use of environmental cube-maps. One of the other highlights is definitely the animation system, in particular the facial animation and lip-syncing.
The story leaves plenty of things for you to infer on your own, but that has always been Half-Life’s approach.
Highly recommended.
(Plenty of other games left to play — this one jumped the queue so to speak )