Geometrical differences of subduction zones
Differences in subduction geometry depend mostly on what type crust takes part in the collision (oceanic to oceanic, continent to continent, oceanic to continent), the speed of the two (or three) colliding parts and the relative movement of the two plates.
Many subduction zones share similar characteristics (like back arc compression and volcanic arc) but there are many differences too. The general geometry of a subduction zone is, in general, well understood, but there are still many questions about how, why and when, mostly because most of our measurements are indirect and the interpretation is still problematic. You can read http://www.platetectonics.com/book/index.asp for a very good and simplified explanation of tectonic plate movement.