After you reach safety, Half-Life 2 settles into a more conventional and familiar style of play. Aside from a detour through a deserted town full of all sorts of booby traps, there are a lot of echoes of the original Half-Life in Half-Life 2--so many, in fact, that there's a strong sense of déjà vu at times. Still, it's hard to knock Valve for not wanting to tinker too much with a proven formula, and Half-Life 2 is as fast-paced and enjoyable as its predecessor.

Clad in your rugged hazard suit, you'll battle your way forward against all manner of enemies, only to recover quickly by picking up health packs and recharging your hazard suit at energy stations. Some of these foes are familiar, such as the headcrab and the barnacle, while others, like the manhacks (essentially flying buzz saws) present whole new challenges. Meanwhile, you'll be armed with a formidable arsenal, most of which is recycled from the first game, such as the submachine gun, shotgun, crossbow, and, of course, the ubiquitous crowbar. These weapons haven't changed much, and they feel roughly the same. There are only three new weapons, including the pulse rifle, which is a sort of beefed-up energy rifle with a devastating secondary attack and a meaty sound to it. Much more fun are the pheropod--otherwise known as "bug bait"--which allows you to summon and control vicious ant lions, and the gravity gun, which can be used to pick up and manipulate objects.

The gravity gun is one of the great new features introduced by the game. Thanks to the new physics engine, it has all sorts of applications in and out of combat, and you'll spend a lot of time tinkering around with it. It's just as useful for picking up and hurling a grenade back at an enemy as it is for solving any number of puzzles in the game. Most of these puzzles are clever but not too difficult, particularly if you've played previous shooters, like the original Half-Life. Half-Life 2 also features a fair number of jumping puzzles, though nothing on the frustration level of Xen in the original game. The jumping puzzles are a weakness in Half-Life 2, but thankfully you can take a more aggressive approach and bypass most of the jumping altogether.

The other noteworthy additions to the gameplay are vehicles, specifically an airboat and a high-speed buggy. While these sequences offer a visual rush, they're also not too far removed from some of the rail sequences in the original Half-Life. In many instances, you'll be funneled down a narrow channel or road with little chance to explore or veer off the beaten path, battling enemies in a high-speed engagement. You'll then encounter an obstacle that requires you to jump out of your vehicle and solve a puzzle to proceed. The controls and physics in these sequences are a bit loose, but the vehicles are fun to drive, especially when you get some room to maneuver.

You'll be on your own during most of the game, but there are levels in which you'll have the opportunity to fight alongside allies, both alien and human. Some of the best team moments come later in the game, when you're battling the Combine in the streets and buildings of City 17, with large-scale battles going on between groups of humans and the Combine's huge, spiderlike striders. You never really develop any attachment to your teammates, though, as they tend to be very disposable, and replacements are available at regular intervals. And teammates have a tendency to get in your way in cramped interiors--while they'll slowly move out of your way, it's still a little annoying. In addition to taking on teammates, you'll occasionally have the opportunity to set up sentry guns to assist you in defense. The toughest sequence that we encountered in the game involved setting up a handful of sentry guns in a defensive alignment, and then holding out against waves of incoming Combine soldiers.