It was written in the idiom of the time, and the people of the time seemed able to read it without becoming bored. When I read, 40+ years ago, I was not a person of the time. I read it packaged with The Mysteries of Udolfo by Ann Radcliffe, which was better; The Old English Baron by Clara Reeves, which was also better; three other shorter works and Carmilla by J. S. Le Fanu, which was terrific.
Anyway, I suspect what you're asking, Baylor, has already been done, sort of. Branching off of ...Otranto was the mystery genre, the horror genre, and all the Gothic romances you could ever want. Also, maybe, Scooby Doo (see, there's a rational explanation for all of this ...). [If you want a fun read, try to find John Dickson Carr's The Burning Court if you haven't already. Two endings, one rational, the other less so.]
As I recall the devices used in Otranto are so old hat now they would be difficult to freshen up. You'd probably have to bring them into the present day, or try writing a Gothic of your own and disguising that it was Otranto rewritten.
Randy M.