editI find that guns matter a lot as to how you perform. lol. I mean, playing recon w/lieutenant is awesome. I just use the rifle, and I can easily sneak up, and kill them before they can even turn around. Assaults included. Support, maybe a bit more challenging but still manageable as they are slow. Hell, recons are harder to kill. However, playing recon with just the p90 is pretty bad. I mean when the support or assault can kill you in 1/4 of the time it takes for you to kill them, you're probably going to die a lot.
I find it best to start out as support. With basic weapons early on, the hitpoints matter a lot. Then once you get the blue rifle thingy as assault, use it. Then once lieutenant go recon.
Great game though. I love the vision modes. Night vision is a bit useless imo. Haven't played a map where I can actually use it effectively. Thermal is awesome, and so is motion.
edit: I generally start as support and use the zr-68, then switch to the MX-5, then go assault and use MX-5 suppressed. Then keep using that until I reach lieutenant and use the eitehr mx5 or zr-68. Whichever one is usable by the recon.
Haven't tried out too many weapons yet though.
2nd edit: kinda makes me sad, but their are a ton of hackers. Chams/wallhack etc.