I haven't played Minish Cap very extensively, but if this is an arrangemnt of a portion of Vaati's castle, then I can tell you that Vaati's castle is, itself, a rearrangement of Hyrule Castle from The Legend of Zelda: A Link to the Past.
If you give that one an ear, then you'll understand why I think this really needs more energy. Darkness does not mean a slow song. There are some very full, dark, brooding tracks. Have a listen to Metallica's S&M The Call oh Ktulu. There is so much shit going on in that track it is not even funny, and it is brooding.