I have run I10 a couple of times and mostly enjoyed it. First time I ran it concurrently with I6, flipping back and forth between the two. Although atmospheric, this was also very confusing and tended to dilute the impact of both adventures. The second time I ran it, I used it as a direct sequel to I6. I played Strahd to the hilt in I6 and managed to pull off a TPK without any fudging. I then had the PCs awaken in the Sanatarium in Mordentshire as per the opening of I10 and proceeded with I10 more or less as written.
Played as a sequel, it was far more effective. The feelings of horror the players experienced upon encountering the normal version of Strahd were very effective and there was an overriding atmosphere of tense paranoia througout, especially when the body-swapping was uncovered.
I and my players found the ending somewhat contrived, however, so you might want to give the players some more freedom in that regard, but it worked overall and we were able to overlook the railroad aspects of the adventure in favour of the pretty compelling plot.