Old Forgotten Game Mechanics

[Avenger]

What do you guys think? Do some of your old favorites have such amazingly fun game mechanics that you can't beleive haven't been replicated or totally ripped off by now? Maybe even something done in 2D that could be trasfered into an awesome 3D mechanic?

[BocoDragon]

I'd love to see Megaman X's wall slide thingy replicated in 3D... Not a wall jump, but a grippy slide down every vertical surface, which could be used for wall jumping, even up one wall.