Ring Cycle - A very obscure voxel exploration game based on Wagner's opera 

Also Lands of Lore 3 is very unique, especially for rpg of the time, combinig high detail shadow maps world with 3 d voxel sprite characters, every with own voice overs and gestures.

As other voxel, but not voxel space games, try Savage Warriors and Hexplore

Except voxel space -like terrain, also not so common polygon characters