Glad you liked it!
I agree, I toyed with ideas of changing key and such but I think I was mostly focused on making it a seamless piece without the usual obvious cadences at the end of every variation. I'm glad you noticed the theme intertwined with the transitions!
Very dark mood that kept me listening all the way! I like the unexpeted chromatic changes and I agree it's very rhapsodic. I'm not sure what's happening at 3:42- 3:48, very low notes? Superb piece!