I find that new lenses are very sterile. Yes, they perform well, they are very sharp and predictable (all very good things) but they lack character.
Older lenses are less optimized, but their technical, objective shortcomings accumulate into something greater than the something you can really summarize easily. I'm sure that optical engineers could look at how a lens performs and predict exactly what aberrations are at play that contribute to the "look" of a given lens, but often these flaws interact in a way that gives a lens an interesting quality that is intentionally minimized using today's computer-aided optimizations.
OTOH the Olympus OM 50/1.4 I owned was so outrageous that it was hard to predict how to use it.