Favorite Mechanics?

As astudent in game development, let me ask you guys about your favorite gameplay mechanics: whole genre, small gameplay elements or whatever you experienced as fun, let me know :D

I like, for combat at least anyway, hack and slash style game play that have something more to them if you put the time in. That way I can have fun mashing X (or whatever) but then go back through the game and play a bit more 'flashy'. It sometimes makes it feel like a new game. I'm also a big fan of action adventure games, but some of them are not so friendly on us casuals hammering one button haha.

I like turn based RPGs, 2D games with good use of rastering and compositing and occasional 3D effects ( IE, Symphony of the Night )