I watched the Blu-rays on a 7' wide front projection screen (Full HD) and despite the large image I couldn't really see production screw-ups except for the occasional seams at Spock's ears (and I only paid attention after
it had been mentioned here).
One of the great things about HD resolution is the sharpness that gives the images such a "live" feel that you actually do wonder if they shot this a week ago. To me the whole thing had characteristics of a time travel experience into the future.
My biggest issue with DVDs has and always will be that the MPEG-2 data compression is sacrifying a lot of color fidelity.
Considering how colorful the original show was (at least from the director's point of view), DVD betrays a lot of these colors while the Blu-rays don't (however, it did seem to me - "Journey to Babel" murdered Tellarite scene! - that in the latest restoration they didn't get these colors always right).