Limits make everything more fun!
I have this thing I call the Nintendo Theory(tm). Nintendo was great at producing games that were simple, responsive, and had endearing characters. Companies like Microsoft and Sony pursue complex graphics and complex controls and they make amazing feats of technical engineering but if you ask people what games they absolutely love, a lot of them will say they love the old Nintendo stuff.
I try to apply Nintendo's approach when I'm thinking about and designing the user interface for my app.
I suck at Mario, by the way, but I love it.