It's a strong finale, too. The generator needs to be started and then restarted mid-siege, but it's on the ground, which is easily assaulted from every direction. The generator powers a lift inside a warehouse that holds your ticket out of Crash Course - a reinforced truck, which it lowers in agonising slow-motion - but even if you spend the bare minimum of time outside and use an internal stairway to reach a low roof, you can rely on infected assaulting you through the double doors behind you and climbing up on three sides as well. Hunters and Smokers can also pick you off quite happily from surrounding rooftops.
There are more weapon and ammo drops in Crash Course than usual, but you can understand why, because it's a proper day out for the special infected, who can spawn delightfully close to the survivors thanks to cover from abandoned cars and lorries, and are rarely more than a few metres from their targets if they want to enter the fray from the safety of a rooftop. The patch that preceded Crash Course also introduced new HUD elements for the special infected - cooldown icons that show you which of your team-mates' abilities are available and which are recharging. Particularly useful if you're, say, a Smoker hoping to grab onto a Boomer's bile-covered victim and want to check whether the big man has a gob ready to go.
There's an Achievement for hauling in a bile-covered survivor, along with another for incapacitating three survivors as a team within five seconds of each other, and some lower-hanging fruit like restarting the generator within 30 seconds of it going off during the finale. You can certainly obtain a good chunk of the extra 250 gamerpoints if you're playing on Xbox 360 without having to grind or pray, but some will evidently take more time and effort - like the one for killing 5359 zombies on Crash Course alone, reminiscent of the ludicrous Zombie Genocidest offering in the main game.
How well Crash Course operates for truly hardcore Versus mode fans is something it would be stretching credibility for me to address: I've played plenty of Versus, but having been in a semi-decent Counter-Strike league a long time ago I know that things are very different when it gets serious, especially this long after release. Still, you sense those people will need no convincing anyway, and many of them will be playing on the free PC version too, where critical commentary would be as meaningless as a mouse without built-in sensitivity adjustments.
For the rest of you - people who loved Left 4 Dead on either format - Crash Course is another strong, if understated slab of zombie-smashing from the people who wouldn't be told that a four-player FPS that lasts four hours was commercial suicide. In 24 hours I've already gone through it nearly a dozen times in various modes on Xbox 360, and I don't regret parting with five quid for the privilege (in fact, it was mis-priced at 800 MSP when I bought it, and I don't regret that either). Those on an extremely tight budget might want to put those pennies towards the fantastic Left 4 Dead 2 instead, but if you have a hankering now then you'll find Crash Course grows on you. Gob you later.
Left 4 Dead: Crash Course is free on PC and costs 560 Microsoft Points on Xbox 360.