Infinite Dungeons 3, even if it never got finished. The combat was epic, the style was epic, the dungeons themselves were epic (they eventually got ported to ID2)... I can't name every last cool thing.
Being able to create a project of your own is an intrinsically fascinating experience, though for many creators becomes tiresome and arduous. Programs and games that help to simplify the creative process are so widely sought after because they provide a simple outlet for building and presenting...