Why are there no isometric adventure games?
It’s interesting that no or nearly no adventure games have used the isometric perspective, or rather, the game system that comes with it. The only exception I know is the rather unconventional Sanitarium.
This is strange because many of the isometric RPGs of the late 90s (especially the Fallout games) have strong adventure elements. Dialog trees and inventory-based puzzles go well with this type of engine. But adventure games have moved from the old 2D room view either to a gameplay-wise identical 3D room view (The Longest Journey) or to a full 3D environment (Gabriel Knight 3).
This may be one reason for the decline of adventure games in the second half of the 90s: They had stopped evolving. They moved well from parser-based text interfaces to graphical point-and-click interfaces (and contributed some of the best graphics in the 320-pixel-era), but then they got stuck. The live actor/full motion video thing was a dead end, and did not contribute anything to gameplay anyway. And the possibilities the 3D environment was not utilized either. As one critic of Gabriel Knight 3 remarked, you can crouch, but what for? It’s not as if there were a note hidden under a bed anywhere in the game.