For many years I wrote games for different PDAs, mostly iPAQ and thought I easily could translate this knowledge to Android smartphones. Now I have learned that even if they look the same there is a huge difference. A PDA uses a stylus (a small pen like input devise) and smartphones uses fingers.
This does not sound like a big thing but it is! The first thing is that buttons must be much bigger on smartphones. On a PDA they could be 16x16 pixels but on a smartphone they must me at lest 50x50 pixels. The other thing is that without a stylus people tend to be lacy and the games must be much easier. Then there are other differences like the different screen sizes, higher resolution, different programming languages and the way the games are distributed but these are minor problems.