Torchlight is a very simple game UI wise (only one character to control, very limited inventory managed and interactivity with the world, character could easily be moved around the world with direction keys instead of a mouse if need be, limited number of abilities that can be put on the UI, etc). I didn't like Diablo one bit and as such have stayed away from Diablo 2 and 3 and most of their clones (Torchlight being a notable exception) so I can't comment on those.
In what way (regarding to the controls) is Baldurs Gate more complicated in world interaction than Diablo and other ARPGs? You just point and click on things. It´s just the number of NPCs, Items, dialogue-options or whatever that is increasing. The kind of interaction is the same still the same: Point and Click.
Even the number of characters is no problem. It should be possible to switch between the characters with one button.