Adventure games, I think, have more untapped potential than any other genre. However, they seem to have gotten stuck in the 'guess what the developer wants you to do' rut. It's like reading a book and not getting to read the rest of it until you guess what the character's supposed to do. And in some games, if you guess wrong, you have to reread a few pages.
Lame.
I think the solution is that adventure games shouldn't rely so much on 'use item with something else' to continue, AND they should do it better when they do. Look at Zelda. You see a cracked wall, what do you do? Everyone knows you use a bomb on it. What makes it interesting are times like in link to the past, that one wall that you could bomb, but there didn't seem to be any way to get to it because of a gap in the floor.
The important part is that it wasn't necessary at all. The game didn't stop there if you couldn't get to it, but you were rewarded if you could - and you were driven crazy if you couldn't, which would make you want to get to it more.
Adventure games are practically made ENTIRELY of game-stoppers. That's not fun. Or really a game. I suppose you could call it a guessing game, but there's no element of skill, and the actual gameplay isn't fun. All the witty writing in the world isn't enough to make up for bad gameplay, and that's why I think the adventure genre tanked.
Summary: For adventure games to improve, they need to have gameplay other than guessing what to do, because not knowing what to do next is high on the list of gamer gripes, and making a game based on that is ridiculous.