Another surprise is the somewhat disappointing performance by the game's artificial intelligence. Even on the tougher difficulty levels, most of the humanoid enemies don't seem to show the same kind of intelligent behavior that they did in the previous game. They'll seek cover and then peek out to fire, but invariably they'll charge at you, making it easy to take them down. And maybe it's due to some of the weapons being a bit overpowered, but most opponents don't present much of a challenge at all--a few rounds is usually enough to stop them. There are a few fearsome foes in the game, not the least of which are the larger ant lions, which will tirelessly pursue you while you frantically unload every bullet you have at them. Then there's the strider, the 50-foot-tall, walking, organic tank that fires devastating bursts and can spear you with one of its legs if you get too close. But for the most part, Half-Life 2 is a surprisingly easy game, even on the tougher difficulty levels. Case in point is the end of the game, which feels anticlimactic--you're given a horrendously overpowered weapon to use against relatively weak opposition.

Half-Life 2 uses a checkpoint save system, allowing you to quickly restart at the last checkpoint if you die, and there's usually a checkpoint right before most of the game's combat zones. The checkpoint system is effectively employed throughout most of the game, and it allows you to immerse yourself into the experience without having to worry about saving the game constantly. Saving the game manually is an option, and it's helpful in one or two passages where the checkpoints are spaced too far apart, but it also takes you out of the moment.

Half-Life 2's presentation is extraordinary, thanks to the new Source engine. Even though Half-Life 2 debuted a year later than originally anticipated, it is still very much a cutting-edge game, featuring state-of-the-art graphics technology. While Doom 3 features superior lighting and shadowing, it didn't really succeed at bringing a credible and cohesive world to life. Half-Life 2 does, and the environments in the game are simply stunning, from the plazas and streets of City 17 to the rusted interiors of an abandoned factory. There's also some excellent level design in the game, including a deserted town full of deadly traps and the gaping interiors of an alien citadel. The engine does a great job of rendering both indoor and outdoor environments, and there's a lot of eye candy to absorb if you have the hardware to handle it. Most surfaces nearly glisten with the latest shader effects, and the textures are sharp and richly detailed.

One of the big new features is the incorporation of physics into the engine, and that has an effect on the visuals as well. Basically, everything moves and behaves as it ought to, so when you hammer a strider or a gunship with a rocket, it shudders and recoils from the impact. Characters also move in a lifelike manner, and the animations are smooth and believable. You'll also discover that objects in the environment can be used against you--there's nothing that zombies like more than to hurl a metal barrel in your direction. On the other hand, you can use the gravity gun to hurl objects about, or even to pick things up and use them as a shield.

While Gordon Freeman doesn't say anything, you'll quickly discover that some of the best parts of the game are when a character has a one-sided conversation with you. This also lets Valve showcase its remarkable new facial technology, which brings human characters to life like never before. You can literally see the gleam in characters' eyes when they speak, and they can display a wide range of emotions, from fear to familial pride. It also helps that Valve enlisted notable talent to supply the voices for many characters, including Robert Guillaume, Louis Gossett Jr., Robert Culp, and Michelle Forbes. The voice acting is superb, and the script itself features wit, warmth, and humor.

The sound effects are also well done. Once again, it's the little details that stand out, like the buzzing noise of manhacks as they approach and the clatter of a gutter pipe as something climbs up to reach you. As in the original game, there's very little music, and what's here is electronic in nature and reserved to emphasize important moments, such as when you're headed for a showdown with a major foe. Most of the music is forgettable, but there are a few standout themes, one of which is recycled from the original game.

Meanwhile, the multiplayer aspect of Half-Life is veritably a game in and of itself.