[After a brisk nap]

Yeah, based on your requirements, WME seems like the best bet.

Of course, you could always use a general-purpose engine like Torque, but it would probably be more work because you would have to implement many adventure game concepts yourself. Or you could try to ask a suitable development studio if you could borrow their engine.

But if you don't have any major issues with Wintermute, that's what I would go with.