I'll just lay this out simple for you guys.

When you first start up the game, you will hardly have any characters unlocked. This is where you either:

A ) Play the Campaign

B ) Level up in Multiplayer and wait for new clothes in between receiving new abilities and taunts.

The main way to get some cool outfits is to play campaign, as you progress through it you will collect mystery (?) boxes, at the end of each Chapter at the Record screen showing your completion rank and stats, it will give you the option to open up your Mystery (?) boxes, these will either give you Credits, which can be used to buy new swag, or unlock clothes, taunts, or abilities.

In Multiplayer, as you level up you receive new things. (Close to the way the original Lost Planet system works). I've also heard some stuff about challenges you can complete for titles, and I think new items, although not fully sure.

Also titles are like Nicknames, but they describe the way you play. For instance if you use the rocket launcher a lot it gives you a title having to do with that.

Also there are some cool challenges, like making jump shots with the rocket launcher.  

----Simple, right? Okay, maybe not as simple as I first planned it would be...

I hope that in campaign its possible to play solo with the same amount and strength of enemies as with 4 players on the hardest difficulty.

I hope with all my heart...