From the main menu go over to "Profile" and the default should be the "Unlocks" page.
Scroll down and you'll see all the weapons, maps, and gametypes you can unlock. Level 17 is the max level which you will be able to unlock everything. Which you can level up by doing Online matches (I hosted online matches and double-boxed). Here's the list of Unlocks!
- Sniper (Weapon)
- Back to Basics (Gametype)
- Sword (Weapon)
- Subway (Map)
- King of the Hill (Gametype)
- Rivetrifle (Weapon)
- Swordsmaster (Gametype)
- Lobshot (Weapon)
- Reactor (Map)
- Capture the Flag (Gametype)
- Umbrella (Weapon)
- Disco (Map)
- Shockbow (Weapon)
- Juggernaut (Weapon)
- Arms Race (Gametype)
- Manhunt (Gametype Settings?)