You just gotta get in there and smack them buttons. Them big buttons are fun to tap. I personally don’t draw a distinction between DDR, plastic instruments, and arbitrary button setups (I’ve played nearly as much Amplitude on PS2 as DDR)
Beatmania has always eluded me. I’ve found a few Sound Voltex charts that are crazy fun (and it makes me wish the buttons in the xbox 360 DJ Hero controller were arcade-quality)
Pump It Up can, of course, go to hell.