A brilliant shooter everyone should experience
Left 4 Dead, although not a pure Valve developed game, does exemplify Valve's brilliant track record of outstanding game design brilliantly. This co-op zombie shooter is so exceptionally designed that it should be held up as an example to all potential game developers as a master class in pacing, level and sound design, A.I., and game design in general, because in these categories, few games spring to mind that can top it.
But away from the technical side, Left 4 Dead is an extremely fun game to play. Mowing down zombie horde after zombie horde is extremely visceral and cathartic, and the intensity of some of the battles is remarkable, particularly the encounters with some of the special infected, most notably the intense uber-powerful Tanks. It's also a genuinely scary game; being snuck up on by a Hunter from nowhere is enough to make you jump with fright, and the pained whailings of the Witch perhaps eclipse the Poison Headcrab Zombie from Half-Life 2 in terms of sound effects capable of sending blood-chilling terrors down your spine. The haunting atmosphere established throughout is sublime, so that even when you're not experiencing jump scares, the experience is still very unsettling, as you progress through the levels knowing full well that another zombie horde is only moments away. The effect is profound.
Visually it's also extremely impressive. The levels are well designed, with some extremely neat features such as the incoherent mysterious scribblings from other survivors inside the safe houses. Graphically it looks just as good as any other Source engine game, and frame rate drops are rare, which is especially impressive when one considers the number of zombies the game throws at the survivors in one go. However perhaps the most impressive aspect of the game technically is the A.I. Computer controlled team-mates in most co-op shooters don't feel particularly useful or realistic - one need only point at Army of Two for a perfect example of this - but although Left 4 Dead is at it's best as a shared experience, playing the game single player is still totally viable, thanks to the strong A.I. of your CPU controlled team-mates.
The central concept behind Left 4 Dead accentuates simplicity and a lack of narrative, but still manages to be just as rewarding and immersive. Very little background information is given about the four playable characters - each of whom fits fairly comfortably into a video-game character stereotype - and even less info is given about how the infection arose and spread to such a degree. But despite it's lack of narrative - or perhaps because of it's lack of narrative - Left 4 Dead's central premise is not only extremely well realised, but also believeable, more so than zombie fests such as Resident Evil or even Dead Rising. Yes, the story can be boiled down to just five words - there are zombies, kill them - but that doesn't matter in the slightest.
What does matter however is Left 4 Dead's lack of content, which is undoubtedly it's most substantial weakness, and the principal reason why the game is a 4-star game and no higher. While Left 4 Dead is an extremely tight and technically strong exercise, the fact that there are only four campaigns is problematic. Sure, you can experience each campaign in a different way - alone, local co-op, online co-op and versus - but that doesn't stop the game from feeling repetitive after extensive playing. In that sense Left 4 Dead could almost be considered in the same vein as Portal, a beautifully tight and seamless 3-4 hour fun ride, but the difference is that while Portal was bundled in with The Orange Box, and is also available over Xbox Live Arcade with bonus maps for 1,200 points, Left 4 Dead is a standalone game.
Of course you can play the campaigns as many times as you like and still enjoy yourself; the A.I. Director is designed for just this purpose and to give some originality to each playthrough, and the different ways of experiencing the campaigns also helps this cause. But the sheer lack of content is a sizeable barrier to overcome. It's not as if there is any form of exploration offered; once you know your way through the levels, any mystery of level navigation is completely erradicated. In theory, Left 4 Dead only features 4 hours of original content, as each campaign takes about an hour to complete. That's the same as Portal. On that basis it is perhaps a bit surprising that Left 4 Dead wasn't included in a package along with HL2 Episode Three or other Valve content. But this is just looking at the game at it's most basic; the variety in modes could easily stretch gameplay beyond the 20-hour mark, and, if repetition in games isn't a fatal flaw in your eyes, possibly beyond even the 40-hour mark.
But mocking Left 4 Dead for it's lack of content is doing it a massive disservice, because you could argue that the game provides more thrills and fun than games that offer 20+ hours of original content. It's just something that has to be taken into consideration. Left 4 Dead is an absolute triumph of game development. Turtle Rock and Valve deserve a huge amount of credit for what they have crafted here, which is one of the most intense, atmospheric and exhilerating gaming experiences in recent years.
If you're well into co-op and playing online, you have no reason not to buy Left 4 Dead, because it is such an amazing thrill ride. However, if you're not sold on the co-op gameplay and like to get your money's worth from a game purchase, perhaps renting the game is a better idea, because you should still experience what the game has to offer, even if you don't want to lay down $40 for the priviledge.