Keep in mind, it's still fast paced action, and there's still more tweaking to be done. But if you get the drop on an opponent, you'll almost always kill him if you're a decent shot. It's not like Quake and R1 where he spins around moving at mach 1 and nails you with some super weapon he picked up in the middle of the map. The time it takes to kill someone, depending on weapon and situation, seems to be about double that of CoD4, and as you know everyone still dies quickly out in the open.
It's all a lot more balanced now that you choose your main weapon, which then gives you your secondary weapon and grenade type. As above, I use the Splicer, which also gives me the magnum and air-fuel grenades. This makes the weapon balance and power highly situational, which you can control with good tactics.
Also, grenades seem to be not much of a problem, which is a good thing. Everyone spawns with only one grenade, making it valuable and you can only get more grenades by killing someone with the right grenade type in their inventory, and even then you only get 2 max. The grenades aren't massive killers either, but they have a very definite effect and will still kill in one hit if your enemy does get out of the way. The air fuel being the most deadly since its explosive radius has no drop off, if you're in the cloud, you almost always die, but the thing takes forever to detonate and it's not hard to miss the white cloud of explosive vapor.
The maps, wow, the maps are great. They're huge, but since the objective system sends people to fight over certain things it works. Well, the objective AI needs tweaking as it'll spaz out sometimes, but it works. Each map usually has plenty of different terrains and situations. It also gives the feeling of a bigger battle as, while going to a different objective, you can come across other squads fufilling other objectives that you can try and help out.
Oh, and co-op is amazing, but could also use more tweaking as some objectives are insanely difficult and some boss enemies have glitches or take forever to kill.