Depends entirely on the source material as it always has with Criterion.
Casablanca: Special Edition #73 (1942) [CC1179L] and
Hidden Fortress, The #11 (1958) [CC1111L] both look incredible in my opinion, but then you have something like
Dr. No: Special Edition #124 (1962) [CC1234L] which came out in the 1991 and looks horrible in comparison.
Still, I'd say the average Criterion release (rather it's on LD, DVD or BD) will still look way better than most everything else out there.