You aren't! Celshading fits "lowpoly" really well. 

The shader I used isn't included obviously, that's just the default Cinema4D cel renderer.

You will get much better results in your engine of choice, I'm practically sure of it.

Can't wait to see these little buggers in action, so if anybody actually uses them in a project, please do comment or shoot me a mail, I'd love to see the results!