A few thoughts, in no specific order here, as somebody who uses a Zeiss ML lens and some really nice Nikon glass too;
1) My Zeiss lens (85mm) has a "look" to it I find hard to define, but I like. the closest I can compare too, is I remember years ago on a large format list that guys said that if you took two, 210mm lenses, one Japanese, one German, and if all other stats were the same - such as they where both F5.6, not an F5.6 vs an F9 - that the glass in the two lenses, while equally sharp, had a different effect on a colour film. one might be more saturated, one more contrasty. This observation is completely subjective, so take it with the proverbial grain of salt.
2) I think there is a missing market for good, high quality, manual focus lenses, and I think Zeiss, and even Samyang, are filling that gap. That 8mm Samyang fisheye is a phenominal lens for the price, but am I breaking some sort of taboo mentioning Samyang and Zeiss in the same sentence?
3) I still do some astro-photography, and for years we have all noticed that stars are one of the harshest tests of any optical system, film or digital, is getting sharp, pinpoint stars, which is extremely difficult on any zoom lens, any size, and brand, especially when compared to a good, fixed focal length lens. for example, I use one of those Nikkor 24-70 f2.8 zooms, and as lenses and especially zooms go, it's one of the best lenses I have ever used and I think ever made. But for a sharp, pinpoint star image, my good old 50mm F1.4 Nikkor still produces sharper images than my zoom. We also found that slight telephotos - such as those ranging form 85mm to 105mm, generally speaking, all brands, were the sharpest and most distortion free, all though there were exceptions for both Canon & Nikkor with some of thier big telephotos
I wonder then, just thinking out loud here, when people mention how much sharper their Zeiss is, are they comparing a fixed focal length to a zoom of similar quality, and somehow picking up on those sublte differences?
Bottom line for me was this. I looked at the Nikkor 85mmF1.4, read several reports that it was just as sharp or sharper then the Zeiss, but I went Zeiss anyhow. Why? Because I wanted manual focus and even though you can turn off the auto focus, I find some of these AF lenses are difficult to manually focus; because the Zeiss was cheaper than the Nikkor; and because the Zeiss does have a different "look" to it on the final image. I also looked at the Samyang 85mm, but I have found in many cases, the best place to put your money in photography is your lens first, and everything else second.
for the record, if I had the money, I would pick up a few more Zeiss lenses, but that's just me. I wonder too if the choice of a lens reflects what kind of photographer you are. For exmaple, inteh good old "film days", my favourite cameras were the Nikon FM and FM2, not a F4 or F5 or F6. Even today, i keep my FM2 in good shape.
