I like the concept of portable gaming in general, but I feel too many developers make portable games with the wrong focus: instead of moment-to-moment interactions like platforming and the like, I much prefer adventure games like Phoenix Wright and Hotel Dusk while on the go: investing the player in the experience with words and exploration just works so much better on tiny screens than  "squint and pray" stuff like Mario and Doom in my opinion, but you don't see very many Hotel Dusks out there.