And it looks wonderful. Check out this Super Mario 64 hack: it's called Super Mario & The Missing Memories, and it's being created by someone who goes by MarioHacker14.
The footage makes the game look like it could have easily been an actual level in Super Mario 64, observe:
The level is one out of a whopping 27, each one with its own unique theme and design. Presumably, playing through the level will help the player recover Mario's memories.