It is coming to Steam this monday for free and it looks good. I played the mod (it was a Unreal Tournament 2004 mod) so much and this one with the Source Engine looks amazing. It will be really good game I think. Valve will also release the complete code base for Alien Swarm. This includes updates to the Source engine SDK and full Steamworks integration. If you’ve ever thought about developing a mod on the Source engine with Steamworks, this release provides more insight and examples for using Steamworks in game production.
http://store.steampowered.com/app/630/

Aye. Read about this earlier, and all I can say is "squee!"
Plus, apparently Valve bought Black Cat? So this counts as a "Valve" game, which means Valve will love game long time. I fully expect to see premium DLC campaigns and the like, which means even more missions for me to fail miserably at :p

I really hope they won't be adjusting difficulty to "mainstrem" - Alien Swarm was great because of it's tension and difficulty as well

Glad I didn't buy Alien Breed Impact or Greed: Black Border. Oh, and in before Steam is evil yadda yadda...

Achievements, cloud, captions, stats, VAC, Source SDK. I say this is pretty much a full Valve game.

Rock on, Valve.

hahah.
Will someone really complain that a free game has Steam DRM?
Anyway, I never played the original Alien Swarm, but I'm looking forward to this simply because it looks like Gauntlet with guns.

Yes. I am quite sure that some people will.

If you have UT2004, just play the predecessor. It'll give you a picture and it's also an awesome experience.
As an answer to your question, in original Alien Swarm, there were 2 campaigns (Colony and a Marine vessel - yes, it's very, VERY much inspired in Aliens movie, and it transfers the atmosphere perfectly)

Very exciting news. To those who have experience with the original: do you have to play in 4 player mode or can two players enjoy the game just as much?

you could play the original single-player and bots were pretty decent. So i'd say yeah

Ok, thanks. Looking forward to trying it. :-)

I haven't played it myself but, it says there's a single player mode in this one. So I'd imagine it's like L4D where if there aren't four of you, you get bots instead. Depending on the AI, a mix of bots and real players might be a good thing (as they won't accidentally shoot you or run off solo). But seeing as this is a new version of the game, all we've got is speculation.

Awesome! I also think that they will update the multiplayer system so it's as easy to drop in and out as it is for Left 4 Dead.