2 big flaws not mentioned: cost and manual focus only.
from : http://www.lenstip.com/390.11-Lens_review-Carl_Zeiss_Otus_55_mm_f_1.4_ZE_ZF.2_Summary.html
Pros:
solid, huge and stylish casing,
sensational image quality in the frame centre,
excellent image quality on the edge of the APS-C/DX sensor,
good image quality on the edge of full frame,
good correction of chromatic aberration,
brilliant correction of spherical aberration,
imperceptible distortion,
moderate vignetting on the APS-C/DX sensor,
off-focus images very pleasant to the eye,
very good work against bright light.
Cons:
huge vignetting at the maximum relative aperture on full frame.
As you see the Zeiss Otus 1.4/55 had just one single flaw, the huge vignetting. On the one hand I don’t know any 1.4/50 class lens which wouldn’t feature a high vignetting level on full frame.