I like the TOS Centurions - the way they moved in TOS was their let down, the limitations of actors fumbling around blindly, but such were the technical production difficulties of the day. Their CGI counterparts look very good, and I'd agree the changes were made just to make them look more mechanical and less like "the guy in the suit " the originals were. Having the subtle differences between the pilot and solder (and any other) versions also helps with a touch of realism. I think I prefer the new ones - they're certainly more intimidating with their height, their built-in weapons and claws and the deeper scanner noise. The rendered version on that concept are reminds me too much of the Star Wars medical droid (2-1B or something like that) and doesn't look Cylon - they need to keep the single scanning red light.
As for the semi-hybrid, I agree that while it is clearly meant to be fully flesh covered as Slayer says, I also agree with him and Newman that the concept seems a Terminator rip-off and completely wrecks the new-BSG's recurring and underlying theme of not knowing who your friends and enemies are - it's an allegory of modern terrorism and guerilla warfare as faced in Iraq and Afghanistan, bringing its own sense of paranoia and distrust. If the Cylons already had infiltrators, then the whole new- BSG premise fails to work.