It's a good idea, but as a developer I would not usually focus on making a minigame-game simply because of the divided attention. I had a few bugs in the workout stage where I could fall through the floor or die out of nowhere, and all the other minigames did not feel as polished. In my opnion if you focused more on the actual boxing and maybe like 1 additional minigame to show teh training it would have given you more time to spend polishing those stages.
I really dig the art style though, but it could have been even better if focused on a smaller area