I've played a bit yesterday. Sort of went in without reading up anything. I think most of us did.

Here's some useful stuff:

- Deathmatch can be fun but it's super unbalanced. Predator owns all, because he's fastest, strongest and has most health. Marine is a squishy joke.

- The mode where you have Marines hunting an Alien and whoever kills the Alien, gets to play an Alien is pure awesome.

- Press "Q" to change your vision style. Useful for the darkness that is everywhere.

- Press "F" as Marine to shoot a flare and try to blind others.
Also in normal vision mode you have the motion sensor working which is superb.

- The game is incredibly fast. Maybe it's good to slow it down a bit in server options to like 80/90%.

I'm looking forward to playing some today too!

Nope. It isn't unbalanced, it's... different from normal shooters. It just takes some time to get used to it, because you have to learn the strength and weakness of every species to play this game "balanced". I've played the singleplayer in the past and tried the multiplayer for the first time now. Played as Alien yesterday and killed quite some Predators without problems, but I had severe problems with most marines.

The Alien is extremely fast, can jump about 10 meters high and its tail attack is REALLY powerful (especially if you can land a hit from behind)! Aliens don't give a shit about cloaked predators, because they can smell them (you see a shining, green silhouette of a predator, no matter if he's cloaked or not). With some practice you'll learn to aim and jump at a foe from the ceiling of a very high room (no falling damage for Aliens). If you're good, you''ll kill an Alien or marine before they know what's happening (Predators have too much health to get killed with one or to blows). But Aliens have two major weak spots: Their health and... darkness. Don't start a fight if you can't surprise your enemies and avoid the pitch black darkness. You can switch vision between "smelling" foes OR seeing 2-3 meters in the dark. An Alien in dark, narrow corridors (corridors are problematic anyway) is a pitiful creature. They're no match for a marine and his guns. An Alien in the dark doesn't even know what's hitting it. Oh, and beeing a melee-only fighter is a "weakness" too. If someone spots you from far away, you're toast -.-

edit: Will try the Predator today, because I completely forgot how he was.

I may be totally wrong, because I didn't play much. It's certainly interesting that you felt the other way around :D
When I played Predator I was just one-shotting everyone with some sort of a pipe or spear. Thought to myself 'this isn't fun' and changed to human. Then aliens ate me alive, because they can kill quick while the marines have to shoot and shoot and shoot.