Just to start, I want to make it clear that the first Half-Life stole my soul. I played it on My old 166, and it is still one of my favorite games.
That said, I had ENORMOUS expectations for the sequel. The best part is, it was actually better than I had expected!
The graphics are some of the best I've ever seen. The characters move, gesture, and even lip-synch just as well as any real human being. The water effect is amazing, and driving along the coast in the later parts of the game provided some almost postcard-worthy views. The physics are also some of the most incredible I've ever seen in a game.
As for gameplay, I found the game to be well balanced, intense, and packed with action. The beginning is, sadly, a little slow, but that serves as a sort of introduction, so it's forgiveable. And did I mention the physics? The game gives you the ability to pick up and throw around pretty much anything in the game, and the later addition of the gravity gun adds to the fun, and not to mention the strategy!
I had a few minor quibbles, though. Steam tends to run you through some loops. You install the game, YOU MUST REGISTER IT. Then you have to wait while Steam DECRYPTS THE GAME FILES! As well, you have to launch Steam every time you play the game!
That said, the game manages to rise above the few dificulties, and truly shine as what a shooter is really made of.