I was debating with myself for about a year before I finally decided to buy this lens. It is a very specialized lens and can't be used that often. At least that's what I initially thought about this lens.
Very sharp in the center; rivals the best primes !! (well it is a prime too; It is very close focusing - 14cm- and with the extreme depth of field you can shot pictures from literally inside flowers; Max aperture of 2.8 comes handy shooting in the twilight zone
CA - but can be easily corrected in PS-ACR; Other than that : NONE; Well; you have to be carefull not to get your hands/feet in the picture but that is not a weakness of the lens; but comes with 180° diagonal coverage