I downloaded it on my Palm over the weekend and indeed, it's pretty fun for a short while. But like almost all Phone games, I get bored of them quick.
It'll be nice when you can get games on your phone that can at least keep your attention as long as a good DS or PSP title are able to (ie Persona 3 Portable, Final Fantasy, etc).
While controls might be an issue for a lot of games, I think you can translate RPGs to touch screens pretty well using touch screen.
We'll see what the future holds though. Gaming on my phone pales in comparison to gaming on an actual handheld still, but getting better.