Hi,
Me and a few buddies played this for a while earlier in the year, go play it immediately it's a quality game. We played for Raven, I wouldn't say PMCs are overpowered but their weapons are different:
Raven - Advanced weaponry and equipment, guns have high accuracy but lack stopping power.
S.V.E.R - Cheap weaponry and equipment, guns have lower accuracy but good stopping power behind them.
Valor - Somewhere in between Raven and S.V.E.R.
If you're used to playing games like CoD and BF, at first you're gonna to be surprised by how difficult it can be to drop people especially as players can heal themselves and others so you'll need to be precise with your shots. I know my KD ratio sky rocketed on CoD and other FPS games after playing MAG for a while. Start playing as soon as you can, it really is an amazing game I'd go back to it if some of my mates hadn't traded it in for Black Ops.