The major strength of Masque is that it puts the Gothic horror of Ravenloft back into its original context: the 19th century.
I completely agree. The Gothic Earth Gazetteer and A Guide to Transylvania were fantastic! Why meddle in obscure demi-planes in the Ether when you can take you PCs to somewhere they think they know and do battle against the original Vampire Lord?
I had the complete opposite reaction. I liked the freedom of a fictional setting. The Gothic earth stuff, while it was interesting, just never clicked with me. I love history, but I had a really hard time getting into the Guide to Transylvania. I think because I was drawn to Ravenloft more for the over the top elements, than by any fidelity to its gothic roots (though it was the thing that got me to start reading gothic horror).
One thing I would argue is that Ravenloft was never really meant to be pure gothic horror. It was really classic horror, drawing a bit on gothic, but also on lovecraft (actually a lot of the horror advice in the black boxed set was drawn from lovecraft), and I think that worked in terms of playability more than if it were rigorously modeled on an academic attempt at doing gothic horror. Not that there isn't gothic horror there, just there is also an awful lot of old horror movie stuff in there too, a lot of camp, a lot of the howling, etc.