Half-Life 2 begins with protagonist Gordon Freeman being thawed out of some sort of cryogenic stasis into a world where the invading alien forces of the first game have taken over and enslaved the Earth. It's also now a world with very nice cutting-edge graphics (by 2005 standards, though the game still looks quite nice today) and an impressive new "ragdoll physics" engine.
However, Gordon's mission, like the core gameplay of the first game, isn't all that different. The biggest difference is that this game sees you mostly spending time outdoors, and travelling between a wide variety of environs rather than being cooped up in a crumbling research facility the entire time. However, it's still basically a game on rails, taking you from one scripted event and impressive set-peice to another in which you blow the hell out of legions of bad guys and take on the occasional light-duty puzzle.
Not that this is really a bad thing. Half-Life 2 is a collection of some of the best set peices, scenarios, character models and weapon types ever seen. Valve also seems to have been really responsive to criticism/complaints about the original game - frustrating insta-death jumping puzzles are nearly completely eliminated, for example (I think there was only one jumping segment in the entire game I had to reload multiple times to get through.) There's also a hell of a lot more squad combat - both with you leading squads of up to 8 grunts, and taking on coordinated squads of enemy troopers. And basic stuff like swimming and ladder-climbing are both much easier to handle and laid out better in the level design.
The game gets off to an excellent start in a very 1984-esque dystopian city called City 17, which is the center of all the game's action. Unarmed, without HEV suit, and completely confused, Gordon is tossed by the G-Man into this world of gas-masked shock troopers (who are quick to wield stun batons when approached) and denim-uniformed "citizens". The best bit of the game might actually be this opening where, after a fortuitous encounter with former Black Mesa cohort Barney Calhoun, the player is turned out into the streets of this Orwell/Wells nightmare without any real idea of what to do or where to go. Of course, following standard Half-Life procedure, one eventually must follow the only available path that isn't blocked, and after a tense unarmed chase scene through a residential complex, Gordon is once again armed, suited up, and the linear blast-a-thon commences.
No time for naps, soldier! On your feet!
The game does pretty well about instituting a wide range of environs without feeling too gimmicky or forced. The opening chapters are most reminiscent of the original game, as Gordon must creep his way through the wrecked underbelly and sewers of City 17 in an attempt to escape and reach a distant resistance outpost. You eventually get hooked up with a hoverboat, however, and there's an extended sequence of alternately jetting down a long river at high speeds and stopping to engage troopers in riverside houses and barns to open gates and clear obstacles on the river. Gordon's time at the rebel base is cut short by an ambush, however, and soon you're forced to flee into the nearby town of Ravenholm, overrun with mutant and alien creatures (and heavily resembling the later Left 4 Dead games.) Ravenholm is a bit more like traditional Half-Life, but it has an interesting twist in that ammo there is extremely scarce, so to get through the thick amounts of baddies Gordon has to employ environmental traps and use the game's new weapon, the Gravity Gun, to pick up and fling loose debris at high speeds as projectiles.
Strike a pose, there's nothing to it
There's another vehicle sequence as Gordon has to travel to a distant enemy outpost to recover an important captured ally, first by driving along a fortified and barricaded stretch of highway in a dune buggy, then working through a Dune-esque beach filled with infinitely spawning giant mutant antlions who pop out and rush you if you so much as set foot on a patch of sand. You eventually raid said base with the help of antlion allies, then return to City 17 for the de rigeur storming of alien baddie HQ. This latter portion features "squad combat" where up to eight resistance fighters can tag along behind you and fight with you.
Most of the game is just butter but it's not without some minor issues. One is that Steam is required to activate the game, update after installing, and has to be connected to to validate the game before playing, even with the Orange Box disc-based version. Aside from being an annoying inconvenience if you have slow (or no) internet connection, the whole install and update portion took nearly an hour on my brand-new computer with a pretty good broadband connection. Fortunately the game never paused for any long updates during the course of playing it over a week, but it's been out long enough now that I guess it's not going to get many. For the most part I find Steam to actually be a good service, but the mandatory check-in at the outset of each game is really tiresome, and you shouldn't have to deal with this if you paid the premium of getting the game on an actual disc.
The second half of the first Half-Life also kinda went downhill with Valve going to the well too many times with annoying insta-death jumping sequences and quick-load battles full of cheap deaths. They've mostly cleaned those things up here, but the lattermost 1/3 of the game is laden down with a few new problems that makes it weaker than the earlier 2/3. The "City 17 Retaking" segment that the game closes out with just feels like an overly long Call Of Dudebro: Urban That Was SIIIIIICK!!!!!11!! match rather than any of the things that made either Half-Life game great up to this point. Valve's go-to source of cheap and easy difficulty in this segment consists almost entirely of "get sniped by lots of high-damage snipers that are hard to reach" and "get rushed by respawning waves of the same type of enemy while holding a fixed position for some contrived reason." This makes the Dudebro part of the game kinda feel like a one-trick pony, and what makes it worse is that your squad AI is both retarted and not at all optional. Guys will just leech on to you whenever you pass them and can't be told to fuck off. You only have two squad commands - basically "stay put right here" and "follow me", but the first one only works while you're within 10 yards or so of the squad, and if you wander off any farther than that they're like "ONOES GORDAN IS GETTING AWAY FOLLOW HIM!!!", so you can't tell them to stay put under cover while you go ahead a little ways and clear out an ambush that you know they'll fuck themselves up in. I'd be more enthused about all the supporting firepower if these guys didn't constantly cluster around you and keep you from strafing and backing into cover quickly, run in front of your rocket shots suddenly, dash ahead and trigger traps/ambushes stupidly, and totally fail to recognize that a grenade landing near them represents a danger that they should make a concerted effort to get away from.
As denoted by the Medal of Awesome, however, Half-Life 2 is worth whatever minor troubles it generates, because everything else about it is excellent and highly enjoyable. The thing that really pushes it over the edge into Awesome grounds, however, is simply the open moddability of it - you're not just getting HL2 when you buy it, but also heaps of quality fan-made mods as well.
* Playable Demo (requires Steam)
* Visual walkthrough
* Concerned - an HL2 comic
* Gameplay Video
* Unbeatable speedrun
* The Combine Interview
* Paper Half-Life 2