The SFX were all really long.
I would use the wall crumbling in some sort of cutscene after a fight but I couldn't imagine it coming up multiple times during combat.
The spell cast sounded very metallic and in-your-face. It would really depend on how frequently the sound is used in the game. If the player was casting spells every second or two it would need to be toned down.
The Den was good ambient background sounds to replace the music in a menu or something. There were a few pops that I wasn't sure was intentional.
Music: Your strings chords in the intro invokes Lord Of The Rings sound track vibes. I liked the buzzy synth At first it sounds like it didn't quite fit, but then I think it goes a good way to being representative of the evil magic. The shakey harmonica is just perfect- someone trying to make themselves feel better but is too scared to play it strongly. Only complaint is that I would have liked it to be able to loop (maybe it would if you chopped off the 45 second intro). This would be good music for voice acted dialogue to be on top of.