Great idea, great composition, great colors!
But, yeah, I agree something's missing. Textures? Can't tell what these guys are made of.
Also, I'm not sure the luminous eyes add that much to the pic. Might look more mysterious without, or more subtle.
It's really flat, but composition and lineart are pretty good. I think you should probably work more on the depth of the piece.
Also think some textues would be cool. I'd say they're made of metal, but not sure.
But, I like the glowing eyes. IMO, this would look boring and uninteresting with flat metal(?) eyes.
Anyway. Really good piece, overall.
I think this is way better than your older pieces.