Having been a lifetime user of Zeiss optics from my Zeiss Ikon, my Contax/Hasselblad SLR days and now using some of those lens with adapters on Canon, I can say they do make some average lens that are based on really old designs like the Sonnar or Planar for their short and middle focal lengths.
Now having said that, one can say that Zeiss has a common problem it shares with many old companies and that they rest on their laurels. They do have some exceptional lens designs, like the Distagons, like my 28mm f/2 and 35mm PC lens. Both have light falloff into the FF corners but there is little to get around this optical phenomenon, and with Photoshop, no real need to either.
Zeiss' Makro-Planars are well regarded by those who have used them, and a 50mm or 100mm version would be on my "to buy" list, if I wasn't already using my old 120mm f/4 from my Hasselblad.
To use a macro lens, you need to be careful to do all you can to reduce shake: Tripod, mirror lock-up and a remote (or self-timer) releases need to be in use.