I've been a DBZ fan for most of my life, so I really adore this painting. Especially since it's Goku and who doesn't love Goku? Anyways, even though I like this painting, there are a few flaws that bother me.
1. I don't expect you to be able to draw like Akira Toriyama, but how you drew his face is very poorly done. His nose is the part that really sticks out the worst. It just doesn't look like him whatsoever.
2. Goku's wristbands, shirt and belt are not the same color. They are always the same shade of blue with his classic outfit. Instead, here you have his shirt colored light blue, one wristband colored light blue and the other a navy blue. His belt is also the same navy blue color as the one wristband or maybe even black. The inconsistency here is terrible.
3. His pinky on his left hand is abnormally long. In fact, all of his fingers on his left hand are not the length they should be. Very unsatisfactory work here.
Although this painting has a few big flaws, It's a very good Goku painting. You drew his body and hair well, and the Super Saiyan energy surrounding him looks fantastic. Just try to focus more on details in the future.