Classic platformer games are always a blast--they're fun, sot of easy and bring back memories (well, if you're old enough, that is).
Two great games on Windows Phone are 'Platformance: Castle Pain' by Magiko Gaming and 'Pixel Man' by Nick Gravelyn. The former is a visually rich, humorous take on an old style of knight rescuing a princess. Filled with tons of traps and difficult jumps, the game is well worth the modest $0.99 (plus a free trial). 'Pixel Man' is a minimalist platformer with simple pixel graphics, but a still challenging adventure. The game looks like something off of an Atari and that's a good thing. That game is also $0.99 but there is a free alternative called 'Pixel Man Zero' which is ad supported--a great option for the casual gamer. And when 5,000 people download 'Pixel Man Zero', Nick's going to release 'Pixel Man 2'--sounds like a challenge.