On Portal 2 co-op - I played split screen with a friend who doesn't normally play games. She loved the humour, and loved the puzzles, but was frustrated as hell by the controls because she'd never played a first person shooter before. So we ended up playing Lara Croft instead and had a great time with that.

It's just a shame that Valve made this smart, funny, non-violent game that could be enjoyed by such a wide variety of people, but is hamstrung by a control scheme that only makes sense to people with a background in FPSs.