14 DAY TRIAL // Left 4 Dead 2 was launched just a week ago and the game already has two new additions, one fan-made and the other official. The fans put their heads together and managed to get the single-player campaign for the original one unlocked in the sequel. It wasn't actually included by the developers in the game, so, if you want to pull this one out, you'll need both the first and the second L4D, as well as a little know-how and that will do it.
The official Source Developer Kit hasn't been released yet by the guys over at Valve, so tinkering with the game is a bit of an elaborate task. But some people managed to do it anyway, and L4DMods.com has a guide on how to do it. To give a quick overview of the process, you'll have to manually edit some files, move them around from the original L4D folder to another one and finally apply the changes via the developer console.
If that made your head spin, you're better off waiting for the official import of the campaign, if it will ever come, or wait for some pre-made mod when it's done. The end result will be that you'll be able to play through the original No Mercy, Death Toll, Dead Air, and Blood Harvest levels of the original with the additional infected and the baseball bat as the melee weapon.
The official content release for the game is the first L4D2 patch and is meant to bring several fixes to the multiplayer. These changes will automatically be applied to the game as soon as you restart your Steam client. The exact modifications are listed below.
Fixed performance problem when rendering lots of decals, notably when fighting tanks with shotguns. Fixed rcon response not working on Linux dedicated servers. Fixed matchmaking problem matching into Advanced and Expert games. Fix bug that would cause other specials to try to pummel a player, a Charger to disconnect or reconnect. Fixed versus mode results in the panel being cut off in transition stats screen in non-English. Found games: fixed non-player entries drawing the wrong type of icon in the selected item name label. Game mode selector on main menu now takes keyboard input.