From everything you've said, SWAT 4 is the game you're looking for, no doubts about it.
Game has a very slow tactical pace with a focus on caution and well thought out planning rather than just run & gun like most other 'tactical' shooters. In Rainbow Six Vegas for example you more or less just shooter everything that moves while the only tactics are whether to dodge behind cover or use grenades or not. In short, it's just a slower paced Gears of War and not terrible clever... fun, I actually enjoy Vegas a fair bit, but it's not tactical. In SWAT 4 however you're not a soldier nor are you fighting an enemy army, you're a police officer. And what that means is that your job is to arrest everyone and *not* kill them. Indeed the game penalizes you if you use deadly force without provocation;
Suspect opens fire on you first, you're allowed to fire back. If they haven't however opened fire, then if you shoot them it could mean a mission failure. This makes for quite a few intense standoff where you're standing there pointing your gun at a suspect and him at you, and you're left wondering whether he's gonna drop it or pump you full of bullets. Intense, but not a situation you want to get into often. The trick is to be tactical, there's that word again, and never give the suspects a chance to raise their weapons even. Flashbangs, CS grenades, Stun grenades, Tazers, beanbag shotguns and pepper ball guns are your best friends since them being non-lethal you're free to open fire as you wish with them.
Oh, and playing this game Co-Op with a buddy or two is some of the most fun and intense gaming you can ever get. Every mission has randomized enemy locations, numbers, and personality so even if you've played a mission a million times it's always an intense experience. It's also perfect for LAN.
Go buy it, now. It's what you're looking for. Guaranteed!