You want short and weird? Check out Crypt Worlds. Free too.

You want a bit longer and weird? Check out Hylics 2. One of the most unique aesthetics in gaming.

You want a very streamlined 3D version of Dwarf Fortress? Try Going Medieval. I have over a hundred hours in it.

You want a Czech version of Duke Nukem 3D with the art style of Quake? Well that's very specific. But good news, you should check out Hrot.

These are all indie games that I think aren't quite as popular as they should be. Not the most explicitly unknown, but definitely under-known.