I was playing about on a Nintendo DS a little while ago and suddenly thought: Wow! you could actually make some pretty cool adventure games on this thing.
Sure you've got the obvious idea of inventory management and stuff but what about some of the other cool stuff?
Lets stop and imagine for a little while... Pretend you're playing some sort of game where you have to copy someones signature on something. Rather than finding someone else to do it you could have a go yourself! Or maybe you want to open someones lock on a house or something. Get yourself some lockpicking tools then actually fiddle about yourself to try and get the lock undone! Or how about the microphone? you might need to get someones attention but can't risk being overheard. You could try whispering into the mic until you get just loud enough for them to notice you but not too loud to attract unwanted attention.
Besides which, they graphics could allow from some SCUMM styled games or even some semi-3D games!
Games can definitely work on a hand-held. Anyone played 'The Fish Files'? If not click here. Not the best adventure game ever but it worked, and worked pretty well.
If people did make adventure games for the Nintendo DS... well, they might not become classic games but they would be different and probably a hell of a lot of fun if made right.