I haven't been too actively working on my own stuff lately; I'd like to, but it seems I mostly don't ahve the time...
anyways, a few things i've done here:
(yes, i know it's a crappy edit.)

The thing is going to be heavy. The best thing i can say, to get a better idea of how a heavy swing should look and feel, swing a baseball bat in front of a mirror. try to stop yourself midswing (and please! don't break the mirror! i don't want to be held responsible if you damage any of your property!) you'll notice that you can't just stop it - there's a little bit of a rocking motion due to the momentum.. Now there won't be as much if you swing something light, like a stick or an empty can of pringles.
so whenever there's a break in the motion of the sing, i had it 'rock' a little bit on the swing preparation, and when it hits the ground.
I've also increased the timing on a few of the frames - specificaly when he reaches a full crouch, and inciden
I've also added a bit more 'blur' when there is a large motion. This is purely my opinion speaking here, but i think it makes the motion look a wee bit smoother.
further emphasizing the heft of the blade, and for increased dramatic effect i've icreased the size of the 'splash' when it hits the ground.
Other than that i don't have much i can offer :\
A couple things i would reccomend doing, which I didn't do here is have the blade land flat on the ground. This has no real life basis, i just think it would look cooler

The other thing, i'd ahve his cape flare up a bit due to the impact, for increased dramatic effect.
one more thing - on the second frame of the part where his sword is behind him, i'd ahve his front leg lift off the ground a bit. not too much or it seems goofy, but i think it would make it look as if he were putting a little more 'juice' in the swing.