Wow well done dude! I've been looking for good Minecraft art for a while xD
This is the kind of stuff I want to see more!
Anyways here is my critique:
-The pose kinda looks silly in my opinion, specially the head; if you are making steve jump in low ground, that pose is not appropriate, since it looks like he is jumping from something really high. The head would be also a problem if he was looking at the ender-dragon from above but with the same pose; it would look kinda derpy.
-The pants have some lines here and there, not sure if you missed them or is that on purpose?
-The hair might not be done but, you should probably ad a little more motion if you can, since he is jumping
+The sword reflection is pretty good, I like it since you can see the reflection light, and the little crystals added in there look great! It looks really natural.
Overall, really good job man! I would love to see more of your artwork in the future