There are a lot of pretty great iPhone games, but none of what I really, really want: old school NES and SNES games playable with real buttons. With the GPad, that's not necessarily the case.
The case slides on over the iPhone and adds all the buttons you need to really play games. The downside? For any game to work with this, it'd need to be specifically programmed for it. But come on, couldn't someone at the very least make an SNES emulator for jailbroken iPhones that works with this? You could then load it up with ROMs and really make it a portable gaming machine. Sigh. Maybe someday.