Quote - And how do I get it???  Poser characters seem to come to life in particular artist's hands.  I am thinking of people like FS, mirrorofsoul, AdamWright, RGUS, louly, Erynn.  It isn't realistic skin or anything like that but it's something else. Eyes or pose or something.  Is it an intangible quality or can it be learned?

Franchesca

I'm still not quite sure what it is you're referring to.  Bear with me on this:

A Character "Coming to Life" means a lot of different things to people.  But, what it really means is that the character/setting flows well and it communicates something about the character that takes a human element to recognize.

You can make a stick figure "come to life."

That's a happy stick figure.  It, apparently, has found a "friend."  It may be a love interest, it may be a parent.. whatever.  The point is, there is something there more than just some lines and squiggles that communicates more than the sum of its parts.  Thus, the stick figure "has come to life."

The quality of a render has absolutely nothing to do with communicating a message UNLESS it is so terribad that its "badness" overshadows any possible message the artist was trying to convey.

IMO, there are a few things that make a human character "come to life."

Facial expression - Too often, people simply have human characters making expressions that a human being is not capable of.  /sigh  There is no possible way some of these expressions could be realized in the real world.. Yet, they get stuck in "realistic renders."  That is a "discordant note" in the artist's work.  If your render is supposed to be realistic, make the expression realistic as well.  That goes for the eyes, especially.  TOO many renders seem to have deadpan eyes, looking at nothing, seeing nothing, revealing.. nothing.    Look at the above stick figure's eyes!  Those have more expression in them than half the realistic renders I saw when doing a search.

Pose - Gravity, gravity, gravity... it exists.  Pay attention to it.  Movement is always about "realistic" movement.  Why?  Look at it this way - You are used to seeing people move a certain way constrained by gravity, their skeleton and simple physics.  Now, in an "unrealistic" render, whacky movements are fine.  Heck, awesome cartoon shows have wacky movements and out of sink motion all the time and it ADDS to the value of the show.  But, ignoring physics doesn't add to anything in a realistic render.  It detracts from it and introduces another "discordant" note.

Match up the theme with the above - That's the "art" part.  For instance, a realistic render that shows a housewife washing dishes with shoulders and elbows somewhat out of realism in her pose, hunched over a sink with completely deadpan eyes and a big smile on her face isn't bad... in fact, it is GOOD if the artist is trying to communicate the physical drudgery and mindlessness that some housewives may feel.  In that composition, the discordant notes actually are significant communicators.  But, if they're not isolated properly or there is too much distraction caused by terribad rendering their nuances will be easily overlooked.

Remove discordant notes in the work or emphasize only the ones that actually convey a message if you're using them for that.  That goes for everything from realistic renders to stick figures.  An artistic work must successfully communicate something more than just the sum of its parts.  If discordant notes and bad rendering overpower any message the artist was trying to communicate, then it is "badly done art."

PS - In the artist's portfolios I quickly browsed, RGUS seemed to have the best nack with human figures and combining good facial expressions, good poses and eyes that "worked" for the image.  Others also did similarly well but RGUS's seemed to be the most consistent.