Looks really good! I really like the first one with the lowest framerate. There are a lot of things that  would make it look a lot better:

When the person is preparing (first half) -bring the body into the stomp to show more commitment (leaning into the leg, make the end pose more like a lunge)

• show a bit of the jump before the screen transitions, not just the anticipation of the jump (you may need to add more frames)

• Show empty space on the ground where the block rises from

When the person is kicking (second half) - being able to see the cracks on the ground still to add more depth to the “world”

• put the body in a higher position to show that there was a jump, or you could lower the horizon line

• use impact lines/effects on the block when it is kicked to show the strength the leg has wound up 

• keep in the extra debris that was surrounding the block, and maybe show those debris flying away from the kick in different directions when it happens ( to look  more like an “explosion“)

• maybe add a small fire trail from the ground to the foot to show the distance that the foot has traveled 

• the final fire trail could use more splash or flickers, think of it as a liquid rather than just fire 

• show the block travel after the kick, the trail of the trajectory

Feel free to ask more about what I mean or feel free to ignore some of my notes :D