ONLINE:
8 Player limit per match.
8 Maps in total.
MAPS: Map Name | size
Asylum | large
Castle | medium
Cliffside | large
Courtyard | small
Dome | small
Hangar medium
Makin | medium
Upheaval | medium
The menus are all pretty nice. Your options are Find a Match, Private match (just select your team, or have it auto-assign), Create a Class (locked), and Barracks (leaderboards etc.)
Find a Match:
Bootcamp (team deathmatch for beginners) - 4-8 players
Team Deathmatch - 4-8 players
Free for All (kill everyone) - 4-8 players
Hardcore Team Deathmatch (locked)
Vereran (locked)
It uses a class system from 1 to 29 (i think, Veteran is 29).
The only mode that I could find players (shouldn't have this problem once it is released) was the free for all. It's pretty awesome. The map I played on was medium sized with lots of cover. There were 4 of us, and there is a little HUD on the upper-right part of the screen (same as in story mode) that shows you the map of the area. You don't feel alone and it doesn't take very long to find someone to kill, and it really doesn't take long for you to get killed yourself.
Also, in the barracks ( leaderboards, there are some stats that can't be unlocked until level 65, so it seems that they go much higher than 29. I am assuming that Veteran mode is deathmatches or free for players at the higher levels. Hardcore TDM is unlocked at level 14, and Veteran at level 29.
There is also a Create a Class option that is unlockable at level 4, but it does not give any info about it.
In Private Match, there are a good amount of options to customize your match.