I'll admit that I'm struggling to appreciate where this Silver Surfer/T-1000/'liquid metal feel/look' comparison is comin' from with regard to Doc Manhattan; that's certainly not an association that I've ever attached to the character.
In fact, the overall effect of his appearance as depicted throughout WATCHMEN is actually the polar opposite of those other two characters, in so much as his 'skin' is in no way shiny nor possessed of a highly reflective, metallic quality... so much so in fact that, in the comics, Doc M's outer epidermis never features any highlights and neither are any shadows cast upon his surface, the inked hatching defining his impressive musculature (so as not to make for a mere flat, uninteresting, 2-D looking drawing) and not providing areas of contrasting shade.
This was clearly a deliberate artistic effect by the creators and cannot simply be attributed to the limitations of mid 80s comic book colouring techniques when WATCHMEN was first published; check out the ABSOLUTE edition with its new, state-of-the-art digitally enhanced colour, and you'll see that Manhattan remains the same, noticably free from shadow and highlight.
It's as if his body actually absorbs light instead of reflecting and so amplifying it, which adds to his overall 'otherworldly' inhuman weirdness, I guess.
Now, I don't know how the hell you'd replicate this effect up on screen, but if it is achievable, then you'd have a character in Dr Manhattan that is truly unique and very distinct from anything that has appeared before in terms of physical looks alone.
