It's funny, I've been seeing the Model S concept in photos around a lot lately, not sure why. But every time I see it I think, wow, the production version looks SO much better! It's obviously subjective, but I think the production car looks better in almost all ways, to me those headlights are a bit too cluttered, the production ones are extremely simple. The wing mirrors on the concept to me are inherently unattractive, but the production mirrors look really phenomenal.
The only thing I wish carried over from the concept is the tail light clusters. They are pretty simple, plain red for the most part on the concept (which is odd considering the cluttered headlights) and in the production car the tail lights are much more.. 'styled', I guess is the word. If the production had the concept tail lights it would be perfectly styled to me. This is not to say the tail lights would stop me buying the car if I was in the position to ;-)
In summary, much prefer the production car to the concept.