Diablo 3

[Mephista]

Act 1: Roamny gypsy-style theme, caravans all over, wise old woman, etc.
Act 2: Middle Eastern. Old-school Perisan style.
Act 3: Indian. No doubt about it. From the gungy Ganges river-clone to the temple-like structure in the middle of town(near Ormus) to Alkor's stereotypical Indian accent(Damnit, I vish you people vould leave me aloone!)
Act 5: No idea. Nomadic tribes come to mind.

Act 3. Indian and yet not quite. It seems to me this jungle region also incorporates some South American elements, so I'd be inclined to call it a fusion of ideas.

Act 5. Seems to borrow from various old European cultures. The Franks were axe throwers, Picts and Celts had the face paint etc. etc.

The temples with very steep stairs is definitely based on mesoamerican architecture. If I ever find my Precolumbian Art and Architecture textbook again (yes, I took crazy humanities classes in college) I'll try to look up similar buildings. The altars and faces in various places strongly resemble mesoamerican art; I don't think they would be found in India. Now I have two reasons to not be a scientist for a while and drag out my architecture books!