This is a bit of an old game but i thought i'd share!
In an effort to find some games that would run on my laptop i dug through my old collection to find Battlefield 2142, by EA. Its part of the Battlefield franchise but set in the year 2142 where 2 factions are fighting over land during the next Ice age. There seems to be some sort of "timeline" to the campaign but i have not been able to find any site with this explained further.
You join a game when the game starts up and as you kill opponents or for full certain objectives (capture, defend, assault, etc) you gain XP, After every rank up you can chose an additional unlock and customise what your soldier will bring into battle for the next round.
If anyone plays this leave a comment below with your characters name and i'll add you as a buddy for a match or 2 :)