Hey Guys,
Played the 360 Demo last night for about 2 hours.
I consider myself to be a fairly experienced Console Multiplayer... especially for a 39 year old.

COD2, COD4, CoD:WaW, COD:MW2, Gears of War 1 and 2, Uncharted: Among Thieves, Killzone 2, etc.
Having stated that... my biggest concern is the default control setups.

I am not a huge fan for using the shoulder buttons as main attack controls. Very unintuitive in my opinion.
However, you do "sort" of adapt to it the more you play. I would love to have user defined or button mapping options.
I did play as all 3 species. The Alien for me was the most fun, then Predator followed by the Marine.
Loved:
-The atmosphere was great, very dark (especially when playing as the Marine), a lot of great ambience.
Looking forward to playing on other maps.
-The speed or frame rate reminded me a lot of Unreal Tournament especially when sprinting!
-And once in a game I was never dropped. Although there was some inordinate amount of time waiting in the Lobbies for players to be found. Probably more due to a lack of people that had downloaded the demo.
-The Predator cloaking was great fun and his vision types were also fun to experiment with.
-The Alien seemed to have the least attack options, but was till the most fun to play.
I would LOVE to have a move for the Alien similar to Batman's AA hanging drop grab! That would be sooo cool in my opinion! (and reminiscent of the scene in ALIEN3).
Disliked:
-The Matchmaking limitations and Lobby. Found it odd to be "kicked" from lobby after each match?
-I hope there are more character model varieties? Via unlockables. Seems to be the case as I remember seeing "Alien Dome" as an unselectable character option.
-Lack of button mapping. I did experiment with the 3 "different" button layouts with mixed results. And when playing as the Alien I did try "Auto-Align" which basically meant the Alien would climb over EVERY surface or piece of geometry that it came into contact with. Default is to use the RT to "force" the Alien to move to another surface. Auto-Align resulted in smother gameplay and transitions, but on occasion it could also cause some serious disorientation if your sprinting through a cluttered environment.
-The grab fatalities, although cool presented 2 problems for me:
1st they can't be countered. I would love to have some kind of QTE button press where you have a second or 2 to "sense" and break/block the grab.
2nd the animations are cool, but they take waaay too loooong. Often resulting in you getting killed by an eager opponent waiting to mop up the mess. To have an option for either a flourishing fatality or a quick kill grab would be a nice.

Akin to the 4 button setup in Gears of War e.g. Neck-Snapping (quick), Curb-stomping(flourish), Bullet Shield(quick), or Chainsaw(flourish).
At first I was extremely skeptical, but in time I came to enjoy the multiplayer.
I am still looking far more forward to the Singleplayer campaigns!
Thanks for taking the time to read this and I hope to see some of you guys online!