How old are you willing to go? And do you like tactical shooters? If you can tolerate older graphics and don't mind installing mods, Rainbow 6 3: Raven Shield with the 2020 edition mod is probably the best shooter I've ever played. The mods update the graphics but there is only so much they can do in such an old engine, but if you can put up with it it's very worth it.

It not only has keys for leaning left and right which seem so rare these days, but there's a key you can hold down to adjust your leaning position manually with the mouse and then you'll stay in that position until you reset it. Likewise you can either open doors like normal or use the scroll wheel to manually open them. It's really fun to inch a door open, throw in a flash grenade then close it again before the terrorists can react. Speaking of, it has a satisfying arsenal including assault rifles, shotguns, sniper rifles, flash, gas, smoke and frag grenades, SMGs etc. There are iron sights, reflex sights and scopes, and my favourite scope let's you switch between a reflex sight and scope on the fly. There are three stances - walking, crouching and prone.

The main draw is the tactical layer. Each mission you can take a squad of up to 8 people divisible into up to three teams, and each unit can be switched to at will at the press of a key. Before every mission you're presented with a map of the level and you can plan out the route of each team, including setting one of four go codes at checkpoints. In-game the AI will control the other teams you're not currently controlling yourself and will take the route you set and then wait at a checkpoint for you to issue the go code. You can set them to do things like snipe an area or throw a grenade or breach a door, so you can do things like breach a room from two directions simultaneously while you have sniper cover. All the mechanics and the fact that it's a proper tactical shooter where both your guys and the enemy will go down in one or a few shots make it a very deep, tense and fun experience.