This lens gets decent reviews around the internet and is usually applauded for its bokeh and being decently sharp. I guess it is, however I am not a huge fan of its out of focus areas. The bokeh can be nice if there is not too much light variation but gets hideous quickly hideous and not smooth at all under some circumstances.
Perhaps the 135mm unit I picked up on ebay for about $30aud is not from a good batch, or the fungus on the front element is affecting it (I doubt it for the bokeh) or my taste is more expensive. For the money it is a good buy, but I would probably advise against using it on a crop, focusing is a little challenging but this could be rectified with a focusing screen.
It is decently sharp when stopped down a bit and is sort of ok wide open, if a little soft. My Vivitar 135mm copy suffers from fairly bad chromatic aberration and ghosting when shooting into the sun. The ghosting may be a result of the fungus on my front element, however due the age and coatings (or lack of) from the time it is possible its just not all that good.
The lens has a dicky little hood that is annoying and cool at the same time and makes me wish there were more lenses with these in production still! Much like the Nikon 135 f2 DC.
Overall I enjoy shooting it but do not think it deserves the praise it receives.