Never judge an artwork by it's program.I've seen some artworks made in 'MS Paint' that would give many people a run for their money.
I like how the flame effects are sort of painted into the image. It's something a bit different and unusual.
The Nike should be moved up a bit so that more of the N is seen. At the moment it looks like Vike.
Under the shoe, I think the painted orange triangle area should be darker so it's more like a shadow. Go for more of a brown colour if you need to.
Lastly, have you thought about a border of any kind.
Sorry for the comments. I do like it, it's just these little things that may take it up a notch or two.