It is a style choice mostly. :) I am fan of old isometric games like Ultima (which was really diametric), and Fallout. Also, simplest to store tilesets when there is no perspective projection - this means they can be rendered once to a larger bitmap for better performance, and that can be scrolled around on its own (versus redrawing thousands of chunks every frame)
Got it. So you couldn't do a view where you could see the horizon or anything due to the performance fixes. The scrolling wouldn't quite work out. It's interesting, I never thought to do it that way. I suppose you could do like spherical deformation postprocessing if you wanted to make this like tiny planets, but then the problem is that the sides wouldn't correctly show perspective. Anyway, it looks great.
You can tilt the view, as shown in the Kickstarter video, with a straight on projection or top down projection - both are difficult to process visually but you can tilt at a higher angle to get a different effect and visibility (might be good if people are crazy enough to try and build a side-scroller with this engine).
