Oh yeah that! I totally agree with you
The level design and enemy placement was 'arcadey' hehe
I wish the unlocking and achievements were a bit more subtle. I understand the logic behind it. They didn't want you using top-of-line equipment right off the bat and they wanted to somehow prolong the replay value of the game.
The more you use a certain style play the more access you to equipment that complements it. For me, I unlocked all the ranged equipment and sniper rifles first since that was my style of play; long range, so I didn't unlock any shotguns close-range stuff till much later.
The CQB (Close Quarters Battle) unlocks came eventually when terrorists would rush me and I'd be forced to use my SMG or pistol. The whole idea is that you unlock the stuff that is relevant to your style. I agree that there must be a better way about it.
The Assault (explosive kills, kill through cover, etc.) unlocks I pretty much earned on multiplayer and terrorist hunts. We went C4 crazy. Laying down C4 traps, door breaches, 'nades, etc.
Honestly, I really miss the original Team Rainbow.