OK, I have both releases from the UK and US and did some side by side comparisons tonight.
I've owned numerous versions of this film from bootleg PAL converted vhs tapes to the Anchor Bay laserdisc and dvd, to several UK and European dvd releases (incliding the rare German Anolis dvd) and recently, the UK Studio Canal Blu-ray/dvd combo. Either UK or new US Blu-ray release is a very good visual presentation of this technically long-neglected film.
First off, they are the same source print, same color timing, same framing. There's even the same Studio Canal intro before the men! There's a noticeable speck of dirt in the lower left off center edge of the frame during the scene in which Barbara Shelley's character Helen is about to "kiss" her brother just before Dracula shows up on the balcony. It's on both blu-ray (and dvd) transfers along with several other noticeable scratches and other very minor blems in the source print. It should be noted that the pre-credits sequence featuring Lee and Cushing is the fixed non-DNR'd versionon the Millenium release present also on the reissued UK Blu-ray.
There is a very small difference in the black levels between the two releases, the UK Studio Canal release is a fraction lighter with a bit more natural grain. The US Millenium release has a bit of black crush and a tiny bit more color saturation and a bit smoother looking picture but nothing to indicate excessive DNR. Strictly from a visual standpoint, the differences between the two releases are really insignificant.
The audio is noticeably more robust on the UK release. I'm sure the US lossy audio track plays a big part in that.
From a packaging standpoint, I prefer the US release with a nice touch of including a small envelope of color lobby card-esque prints. Too bad you have to tear open the envelope to get to them. The slipcase graphics are a bit nicer on the US release too.
The extras appear to be identical between the two releases as well with one key exception - it appears the 8mm behind the scenes footage shot by Francis Matthews' brother is not included on the US release.
Overall, it's a decent first effort for Millenium's Hammer Blu-ray US licenses. Granted it's basically a straight port of the UK release with a smidgen of contrast boosting and different chapter marks, and I will say a near $20 price point is a bit high, but it's a perfectly acceptable alternative for Hammer fans in the US without a all-region Blu-ray player.