That screen isn't exactly suited to most games.
Can you imagine playing Sonic on that thing? They would have to squish the image for you to be able to see where you're going!
On the plus side, it looks like it can work fairly well for 3-D games like Tomb Raider, etc.
It seems that the GBA will have up to 3 more competitors in the coming year... it's amazing what a little competition does to a monopolist company, but we'll see how it goes...