My prediction is marginal improvement in games, but nothing spectacular.
The human interface is simply too limiting and imprecise for good game interaction.
You really only have the screen and the accellerometer to deal with.
If you use the screen, you block half your view.
If the game relies on Tilt, you have essentially a left-right joystick with no buttons.
What could improve this?
Bluetooth mouse support or Bluetooth keyboard support would help a lot.
Baring that, a slim carrier that envelopes the phone, while plugging into the
docking port to provide additional buttons (that are located on the carrier) would
be a solution. Something like this image of a hand-held super nintendo: http://www.geekologie.com/2008/08/04/snes-1.jpg
But lets face it, this device just does not have enough inputs to provide a good gaming experience. The inputs it does have are imprecise and take way too much processing power from the game just trying to figure out what you touched.