Have a look at Voxel Doom – a new GZDoom-based mod that replaces all monsters, weapons, props, and items with fully 3D voxel models.
The models for the mod are created by Cheello, the programming part was done by Nash Muhandes.
The mod is done for the first game, the creators are planning to change models in Doom II "in the very near future." You can see the process of making the 3D objects on Cheello's YouTube channel.