What was the main learning you got from building the engine? Was there some feature you wanted that no other engine at the time had? If you built an engine today, what would you do differently?

I thought most of the existing engines out there were too complicated, so I wanted it to be easy to use. Probably that's also why it became that popular.

For a modern engine today - I think the architecture of the engine would look different - and would focus more on creating and organizing content then mostly on rendering.