This has a lot of things going for it, and there were a lot of things I enjoyed about it. I can understand what people's gripes were with the music selection, but personally it didn't bother me at all. Definitely liked and appreciated when I saw the traditional animation touch, a lot of motions felt fluid, timing and weight felt good. Now that being said there are some things that you could do to improve and take and use for future work. I wasn't worried in the slightest for the hero character. No matter what he was pitted against, I knew he would get out of it with little to no resistance. I would've liked to have seen some crazy obstacles presented in front of this guy. He is going against the God King, who earlier, had completely obliterated all of this guy's brothers and sisters, which would mean he should've been a powerhouse against this one person. I think a much more engaging and rewarding experience for the viewer would be if the hero were sent to hell and back, his limitations realized and overcome all during this battle, I want to care that this guy is fighting for revenge.
As far as the pacing goes for the whole thing, it had its kinks here and there. It felt like things peaked with the battle against the one hydra-like creature. I understand for timing and duration you had to repeat animations and hold on shots a little longer, however you could throw some more variety into it. Those blasts the creature was sending could've has escalated in intensity. Maybe it charges up for a really big one before a spear goes through it's head. You could've had the character get down to his knees from the constant onslaught, or steadily getting pushed back, just something to break the monotony. The final battle against the giant aquatic God King didn't feel quite as impactful as it could have. Maybe throw a thunderstorm in the background, or giant tidal waves. Maybe he uses nature itself AND his creatures to fight this guy. Raise the stakes to give us a wtf moment and we're left wondering how is he gonna get out of this one and for a second we might think, will he? Anyway just some things to consider. I hope it helps and keep animating! :)