Nice! The thing I noticed is that your first sketch is from a more basic perspective. It looks like you used that as a reference for the rest of the sketches, which are from a top-down angle instead. The whole process section is just a really good example of sketching! You didn't worry about making each one perfect, and you made plenty of them to pin down the final look!
The final image is great too, of course. The saturated colors gives it a really cheerful energy-- the exact same energy you'd expect from a game where Master Chief and Vegeta can be in the same squad while shooting Darth Vader to death.