The things that seemed to strain my science sense were:
1) Wallace's cataracts: Like other said these are easily fixed at the present time. They would also be in the future depicted in the movie. On the other hand they were more obvious that real cataracts and seemed to me to be a visual shortcut for saying he is blind. This removes a lot of probably verbal explanation which movie makers don't like.
An associated question would be why was he supposed to be blind anyway? What does it add to the plot? Is it that he is a blind (messed up) guy making, using, and destroying physically (and mentally) better "humans" than he is himself?
2)
Noisy Rhysling said:
So why did they find a serial number on Rachel's bones?
It seemed clear that plot-wise the number was there as a clue for K to find.
I would ask what is the number doing there since my interpretation of their replicant generating procedure was to grow them not to manufacture them. You wouldn't have physical serial numbers on something that is grown. Instead you would have some kind of DNA sequence code unique to an individual. This would be trivial to do since they are genetically engineering the replicants.
Perhaps the Tyrell Corp (which made Rachel) was doing some parts assembly and put a number on her bone. Not clear.
Another question along these lines would be where is the police DNA analysis. This should be pervasive in the future, and useful.
My
previous post had links to what I call background videos for the movie. They cover the
black-out and loss of replicant information, the nature of the new replicants, and the origin of Sopper Morton.
Overall I liked the movie. Although it was long and slow, for me it was absorbing.
The biggest difference for from the original movie was that the first one had a lot of non-obvious things going on which required the audience to think things out to understand. The world in which they the film existed was complex and different which required thought. The most obvious example is whether Deckard was a replicant or not. A similar issue in this one seems to be who is related to whom.
The general theme is the same (to me anyway): "Do Androids Dream of Electric Sheep" or what's going on inside the head of a replicant, should they be treated as humans.