Perhaps it's due to the low resolution of the game, but I've always thought of the phase 1 DTs as DF's equivalent of the Skynet machines in the Terminator movies (see:
http://perso.wanadoo.fr/mdi/images/bckgrd/bckgrd_big/terminator_004.jpg).
So to me they're basically red-eyed metal skeletons, equipped with a shield and sharp protrusion (a la the T-1000's arm in the "milk carton" scene in T2).
That look, coupled with the metallic sneer the DT1 utters when he sees you, provides this particular enemy the menace it needs.
Unfortunately, the DT1 model that is currently available at the DF mod's website IMO looks adorably cute rather than suitably intimidating.
At the very least, it needs a silver metallic makeover (if this is supported by the engine of course).