The collection includes soundtracks for Castlevania games ranging from NES, Game Boy, and MSX releases to more recent games on Game Boy Advance, PS2, and the arcade. Even the spin-off, Kid Dracula, is included on Disc 2! Disc 18 is an "arrange" album, with covers Castlevania tunes by Symphony of the Night composer Michiru Yamane, and disc 19 is a DVD featuring recording studio footage and interviews with Yamane.
It's very unlikely this collection will be officially made available outside of Japan, and if an importer does carry it, you'll have to whip a bunch of candles to scrounge up the coins: Konamistyle prices the collection at ¥21,000 ($232).
[Via Original Sound Version]