A few days ago, I decided to purchase a handheld console and I decided to go with the Nintendo DS. The ultimate factor in the buying decision landed in the games. I couldn't find hardly any games that I had interest in playing on the PSP and I found quite a few that I could see myself toying around with on the DS. So far, I am pretty impressed with the device and it is a joy to have around when I need that intermediate study break.
The touch screen is pretty darn sweet. It definitely goes that extra step to add a different dynamic to the game play. I have a game; 'Mario vs Donkey Kong 2' that relies solely on the touch screen to move around your Mario's to solve the level.
Another tiny feature that I found was its microphone sensitivity to air being blown into it. In the new 'Super Mario Bros', there is a puzzle game that relies on you blowing into the microphone to lift your character. At first, I thought it was being lifted by the noise going through the mic, but sure enough, it was the wind coming from my mouth. Unless it is being activated by noise, but no finger snapping or tapping on the mic did any justice at all. Pretty neat.
Finally, the WiFi. Nothing like sharing the levels that you design and/or playing people from across the world. :)