^_^ the answer is actually more complicated than you'd think...
it is technically a 2D game, however it has a 3d world.
Using a very similar technique to Final Fantasy 7-9 as well as Resident Evil 1-3 ... what happens is first a scene is create in billions of polygons (and yeah i mean BILLIONS)
then it is rendered out in an isolinear view at a 35° angle of view
next a low polygon primative version of the level is then created, and the rendered iso map is then projected by view onto the objects.
the level is then rendered in the same Iso view with pure 2D characters (well 3d plane sprite characters using a modena 360 view thingiemabob) ... finally effects suchas particles and lighting affect the 3D world which is then blended with the texture like most multitexture games, to create very nice lighting effects. And actually if they used a shader they could make most of them hyper realistic.
But capping the veiw and perspective they gain 100% control over what you view and what you don't, which means they can make a beautiful 3D world texture with a specific 3D world to make it look very high poly and very nicely created, yet have none of the expense.
Personally i'd prefer the 360 camera panning around the awekard areas, and possible sequals might be in full 3d for such things. Bar only time will tell if they bother to update ^_^

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