The DSS Cards are the ONE thing I didn't like about CotM. There are 100 combinations, but most of them are either useless or are just gimmicky in a poor attempt to add variety. I mean why would you bother with the Flame Whip or even the Flame Sword? The only worthwhile combinations in my opinion are the Cockatrice and Thunderbird summons, the basic +STR combination, the double Heart drop one, Ice Whip/Sword (for freezing Brain Floats only, useless otherwise), the one that halves your damage at the cost of every hit knocking you back (debatable), the Ice Shield and for enemies with destroyable projectiles, Poison Mist. All of the other combinations are useless or just too gimmicky. It's a huge letdown to have 100 different spells but only have maybe 5 or so be useful with another 5-10 being situational and the rest just there for fluff.
One other thing I didn't like about the cards is that almost ALL OF THE COMBINATIONS rely on your STR to deal damage. Thus, Magician mode is a joke. Sure you have all the cards right off the bat, but without getting all the best STR boosting equipment, they're pathetically weak. Still, set damage ones like Diana + Griffin make the first four bosses a joke.
As for the music, I will agree. Most of it doesn't fit, but then again, I never really cared enough to let it bother me. I almost feel like I'm liking CotM a bit too much and am being that one weirdo that likes it when I should be like "Lol, CotM sucks, 3/10". I sank a massive amount of time into CotM, probably more than I should have.