I played the Ghost of Thornton Hall just before, and I liked that one so much, that I was a little sad to leave Blackrock Island for Glasgow. I find Nancy does her best job in old dusty mansions
The sentimental aspect was nice, but Nancy's usual lack of emotional response was a bit weird here. She discovers terrible truths about her family and the voice acting doesn't reflect that. Meeting Moira should also be an intense experience, yet Nancy doesn't seem to go through any strong feelings about that either. (Don't want to explain more to avoid spoilers.) I think the ND series should have stayed away from that storyline, it just doesn't suit the gameplay.
Having only dad and Ned to phone is not very fun either, especially after Deirdre and Savannah in the two previous games. OK dad was needed because of the context, but Ned is a very boring boyfriend (sorry Ned^^).
Now the game itself was captivating, I must say, always something to solve, codes to crack, as you mentioned, the puzzles are good, and very pleasant graphics.
A shame there aren't any fake passers-by in the train station: it feels a little depressing, empty like that, like the metro in Japan in Shadow at water's edge did.
OK I didn't mean to be this negative, the game is really entertaining, even though it won't be one of my favourite (I need my spooky manors :D).