sorry i worded that wrong, u are right i can imagine levels can be made fiendishly difficult by designers.Define taxing?
i meant not taxing like ninzel saiz, as in cause of the camera method (~2.5d) + lack of into the screen depth, theres gonna be a known number of vertices onscreen at anyone time, most likely an order of magnitude less than a fully 3d game, which means each vertice can be afforded a lot more CPU/GPU work