Amazon finally delivered my set yesterday! I've watched the first two discs and can only say I'm quite disappointed from an HD perspective. Although there appears to be a boost to overall contrast and the colours are more vibrant, for me, the show still has that somewhat drab and washed out visual sheen.
There is precious little of what is often described as "HD pop" by professional reviewers, and the image veers toward the downright soft far more often than not - sharpness and detail is particularly noticeable by its absence in close-up shots.
I won't add to the discussion reference the problems with the upscaled FX - as that's been covered by others extensively. Suffice it to say - the problems are certainly there, they are certainly noticeable.
The DTS Master Audio mixes I've heard thus far are pretty good, nothing spectacular, but more than adequate. Dialogue is clear and intelligible.
I have to say though, I haven't revisited ENT Season One in such a studious manner in some time - and honestly - I'm really quite enjoying it!