Before taking any of the following seriously, keep in mind that I know very little about effects or what effects specialists look for in reels and the like.
The fireballs look damn good. The only thing that strikes me as off is that "main projectiles" (sorry can't think of a better term) appear static and don't seem to spin when airborne, which I would have expected. On this note, if you wanted to take it further, it would be awesome if the main projectiles were an irregular shape so that they'd visibly hurtle through the air, shedding chunks of flaming debris as they go. I think the distant collisions and the foremost collision work really well. The second and third last collisions don't work as well IMO, mainly because of how the castle wall shatters.
I know the castle wall is meant to be simple, but there's no getting around the fact that it takes up the vast majority of the frame (especially the foreground)and that it detracts from the otherwise awesome effects work. Even if you were to keep the same geometry but do a proper job of the textures (with displacement mapping for the extreme FG sections of the wall), it would look much better. Along with more reactive camera work (the "camera man " seems to know exactly where and when each projectile will hit), this would really spell the difference between a VFX shot and a VFX test. If this only a test, you might as well give the wall a flat material so nobody mistakenly thinks otherwise.
Overall, the effects work is awesome, but the animation itself seems to be in the awkward gray area between a full shot and a test. Personally I hope you push this further as a full shot, since it really shouldn't be difficult (especially compared to what you've done so far) and I know you're more than capable. Good luck.