Halfway ThereG 25

To unlock this achievement you simply need to reach level 25 out of 50 by gaining experience points. This achievement is not hard to obtain at all considering the many different ways you can gain experience. Gaining experience consists of just playing game types, raking in kills, completing daily challenges or any of the 990 different game challenges that are available. Most challenges have a five level tier that gives you more experience the higher the tier. Here is the experience breakdown by tier:

Tier I - 500 XP
Tier II - 1,000 XP
Tier III - 2,500 XP
Tier IV - 5,000 XP
Tier V - 10,000 XP