Let me just say the multiplayer is awesome. I have this for the xbox 360, and I've heard some complaints that the aiming was too sensitive; well it's not. On default settings It feels the same as any other game. My brother had no complaints, one thing he said was "it's good that it controls just like COD4", and he's a huge PC FPS player (used to play professionally with a clan). Anyway, onto all the details (underlined important info).

WEAPONS:

If anyone doesn't know about the loadout menu, how it works is you get 15 points to spend on equipment. Everything costs a certain amount of points. Example: Burst-fire rifle for 7 points, medium armor for 4 points, a medkit 3 points, and then one shock grenade for 1 point.
You get 3 loadouts that you can customize and save. You can change between them during a game, and can also edit them mid-game.
You can carry two primary weapons, and can have more than one grenade type at once.

Now I'm not going to go into specifics here because it would be too long, but I've used almost every weapon and they're all solid. I'll go over the 3 weapons that I use in my loadouts. The nailgun is very powerful at medium range; hold the trigger down and aim for the head; much fun nailing people to walls. The burst-fire assault rifle can get headshots, but is a bad choice for close range fights. The SMG is good for close range, but it's hard to kill at medium range with it.

Power Weapons:

These are scattered throughout the maps, and are on a respawn timer.
The flamethrower fires in bursts. It actually fires pretty far, and it kills very fast if you hit them directly. Very fun to set people on fire!
The pulse gun is the replacement for the railgun from FEAR 1. It doesn't go ZAP, instead it's like a grenade launcher that will fire a glowing blue ball that will explode and blast the flesh off anyone nearby.
Rocket launcher can fire 2 rockets before reloading, it's accurate and is very deadly. You will run very slowly with this weapon out though.
I only got the use the laser gun briefly, it seems like a decent medium range to close range weapon. I only got to use it long range, and it's pretty hard to keep a laser on someone from there.

Gametypes:

All are fun, I recommend you give them all a shot, not hard to figure out what's going on.

Control is my favourite. You have to control different points on the map to earn points, like a battlefield game sort of.

Armored Front is great, there are 5 points and you must capture them one by one and hold all at the same time to win. The EPAs (elite powered armor, or mech) are in this gamemode! Very frightening, think of them like a tank compared to infantry. When you enter one, it's very loud and you lose your mini map, so press the Y button (xbox 360) to bring up the map to see where to go. People will be turned into red mist when you fire at them, it's great. When two mechs go at it, it's just really crazy to watch. When on foot, I'd just stand back and watch them go at it.

Blitz is like capture the flag, only they're called PHLAGs. One team must capture the PHLAGs and bring them to the capture point, while the other tries to stop them. Then the teams swap sides. Whichever team captured the most PHLAGs wins.

Failsafe is definitely one of my favourites. It's like search and destroy. There are no respawns in this gametype. One team must plant the bomb in one of the bomb sites, other team defends. To win, blow it up or defuse the bomb, or kill off the other team.

Team Deatmatch plays how you'd expect it to. Good old fashioned fun, and Deathmatch is the same thing except a free-for-all.

Ranked and Player Matches:

There's quick match (which is basically matchmaking I guess) or you can search for a custom game, which allows you to search for a specific gametype or map, then it gives you a list of servers.
You can host a game, ranked or unranked. When hosting ranked, you can decide what gametype, map, and the number of players. Hosting unranked you get all that and more, such as friendly fire settings (it's always off in ranked), round time, damage reflection (?), team balancing, etc.
In unranked games you can invite friends and change teams so as to be on the same team. In ranked games you can't invite friends, but no matter because it's server browsing. My brother and I were in private chat; I tell him to join the Control game with 3 players in it already, on the Revolver map, for example. To be sure to get on the same team I'd wait for someone else to join the other team to make it uneven. Easy as that, we played ranked together all day no problems. Keep in mind, after a ranked game it boots you back out (think Gears of War or Rainbow Six Vegas). In a player match I assume you can play all day in the same server, but never tried player matches yet.

That's about it then. Got any questions, I will try to answer them. Of course, you all will be getting this game very soon anyway, if you don't have it already (I got lucky and my EB Games got it today).

Oh. Not Members of Parliment?

Well never mind then...

The multiplayer is good stuff, very fun.