If not epic, try episodic.
yeah, that's the route I'm planning at the moment. on of my main passions lies in attempting to make stupendous game engines
and I also like grand scale. the episodic route allows alot of flexibility
you can release a single awesome level and call it a demo
several more and make it the first release, pricing them according to the amount of content
if you decide to go that route. you might want to focus on being extremely organized, and also, making your 'engine' as reusable as possible. anything that will be used again and again should be kept in either a template cap, or a level editor, if you have the skillset to create such a thing
it's discouraging to work on the same things over and over again spending more time on boilerplate code and tedium than you do on your wonderous content