(re: What about new sequels?) The GBA has a tile-based 2D graphics hardware, which means side-scrollers are the easiest to do. There is absolutely no dedicated 3D hardware in the GBA, although a few tricks can be used. Any 3D must be calculated in software.
As for true 3D adventure games, I’d say Gabriel Knight 3 is one, or am I missing something?
Also, Shenmue is essentially an adventure game (although is blends other genres) and is incredibly beautiful.
Vincent.