Originally Posted by Demiath
Maybe I'm just stating the bleedingly obvious here, but I think we need to be very careful about how we phrase this complaint. The limit is not in the grid-based structure as such (i.e. that you can only move in four directions); it's that the rigid Dungeon Master formula - and an engine built exclusively to emulate said formula - focuses on Myst-like mechanical puzzles and dungeon mapping and not much else.
In principle, however, you could make a deep story-oriented game like Planescape Torment within a grid-based structure just as easily as a mere Dungeon Master clone (see Irien's comment above). A good example is Wizardry VII, which is more or less an open world game with lots of complex NPC interactions and emergent gameplay possibilities but still grid-based in its perspective and controls.