Why the 'true form' with the weird appearance? Unless perhaps that form came about via sacrificial rituals and thus must contain evidence of such sacrifices to retain power.

For whatever reason, Riddle seems to be planning to do some more stuff with his Voldemort persona; otherwise he wouldn't have summoned his Death Eaters etc. It follows that he needs to keep his pantomime-villain appearance at least in the short term, since that's what his followers expect.

I gather from the last few chapters (though I've suspected for a long time) that he didn't originally intend to look or behave like that long-term, that the form was chosen to match his deliberately over-the-top villain persona, but that he's stuck with it for the time being since the Death Eater thing has evolved beyond his expectations. Perhaps he'll eventually alter himself not to look like Nosferatu crossed with an extra from David Lynch's version of Dune, but that's something you'd want to do after you've reestablished your authority, not immediately after returning from a long absence and the decay of most of your network. Right now, the more Voldemort he can seem, the better.