An incredible first-person shooter that impresses... for the week and a half that it lasts.
The biggest issue I have with HL2 is just installing it: while the actual files took about 15 minutes to load from the disk, it took another 45 minutes to activate it with my glitchy internet connection (something the designers should have anticipated, given that dial-up connections were still pretty common in 2004, HL2's year of release). The fact that Steam continues to check the validity of my purchase just makes me even more irritated.
Once I finally began playing, however, Steam stopped bothering me, and I found myself immersed in the convoluted, worn-out dystopian City 17, it's despondent denizens (with faces so well-rendered you'd swear they were real people: you can actually see the despair and fear in their eyes, the wrinkles on their faces, and the 4'o'clock shadows on unshaven faces), and the incredibly subtle dread that hangs over the entire game. Physics puzzles, boat and buggy rides, wild shoot-outs with zombies and Combine soldiers... the only thing missing were the incredible weapons from HL and Opposing Force...
...that, and the length of the game. Point blank, it's too short. After less than 2 weeks of play, and an abrupt, anti-climactic ending sequence, I felt somewhat cheated compared to the week I spent on the end-game of HL. I understand that Episode 1 and (hopefully) 2 will add more storyline to the core game, but it still feels as if HL2 were somehow abruptly cut off.
If you are going to get HL2, do yourself a huge favor: find a combo-pack with some of the other HL2 spin-offs (like HL: Source or Episode 1) included; otherwise, you'll be done before you feel like you even started.