One thing I noticed between normal and expert is the number of peeping eyes in the first stage (specifically the part before you enter the flooded basement). In normal, there's just one, like in Chronicles. Expert has two. Apart from that, I forgot. I mainly play on expert nowadays.
(rant incoming)
If I can complain about one thing about expert, is that there is no pot roast at all during the whole level. So that means going through the split room, the upside down room, the boss refights, Death, Medusa, Bartley, and all three forms of Dracula on one life is going to be arduous. Stage 3 had the same problem as well (no pot roast). I hate it when a Castlevania game places its pot roast poorly. :/