What games have you played that, regardless of how good the game was, had some concepts or features that you found to be absolutely class?
One game that comes to mind for me is The Mark of Kri. It was an okay game, nothing too special - aside from the battleplay. It's the first game that I feel effectively allows you to fight large groups with fluent attacks. It does this by letting you sweep out with one of the PS2's analogue buttons and selecting up to six characters - two for each of three of the main buttons. So then you can hit the buttons as you like, with Rau (your character) moving swiftly and fluently between the selected enemies, decapitating and impaling as you wish. Best fighting system I've seen in any game of it's kind. And a nice set of combos to go along with it, too. I just wish more of the mainstream games would take it on.
Anyone else know of any brilliant features/concepts/etc. in lesser known games?