Cool game mechanics

[hudson]

Which game mechanics have made you go, "oh wow, that is most cool, sir"?

One mechanic that comes straight to mind, is the camo-meter in Metal Gear Solid 3 Snake Eater.
You can slip into a more beneficial camo frock which matches your current surroundings.

[fishbowlhead]

The true to life physics of puzzles in Half Life 2. Need a ramp? Build it, need a bridge? Build it. Everything just makes so much practical sense.

[endo]

Two games spring to mind as having great mechanics, but they're not so much cool features as key control schemes:

Firstly, the Flick-It control system in the Skate games is a great mechanic. Tricky at first but opens up with perseverance and let's you do pretty much anything you can think of when you master it. Much like skateboarding IRL. I'd never have guessed it was possible to translate skateboarding to a console controller in any sort of meaningful way, but I think the Skate series managed it. I've since played other skateboarding games, with more complex systems, but none has clicked in the same way. I was very pleased to see that the control scheme will return in the new Skate game.

Secondly, the control system in the Trials series is an all-time great mechanic. Simple at first glance but borderline impossible to master. The scope for fine control is huge and, personally speaking, there are few games that are as satisfying as when you nail a super hard course in Trials. One of those games I always end up doing marathon sessions on when I'm only planning to have a quick blast.

[hudson]

I really liked Gambits in FFXII. Basically make a list of instructions for your team mates. Things like, 'if my health is under 50%, then heal me' etc.

Rappel in Rainbow Six. I first remember it from Vegas, but in Siege, I feel you can piss about more freely outside a window whilst rappelling. Being upside down and walking left and right across the wall outside a window trying to peep a shot is just fun. Until someone shoots you up the bum.