Face... The spinal frontier. No, wait. Space... The civil engineer. Aaah, I'm getting old.
Throughout the game you level up your sword and your belt. After each level you collect a grade. After certain amount of grades you unlock the boss fights. These are a bit too easy but also well done, timed just right between the classic 'jump and collect' levels. After each boss fight you unlock a new area and a few challenges with one of the NPC's. Sensei is the only one present at all times; his one-liners never get old.
Collecting all the grades opens a door to the battle arena - not nearly rewarding enough for completing all the levels in all modes. This however is not mandatory to finish the game, so getting 38 out of 64 grades doesn't get tedious at all.
The only real challenge for hardcore gamers will be the last pay-to-compete challenge with the boxing boss on hard difficulty. Some gamers will not like the lack of coherent story and random characters popping out of nowhere but this is a matter of personal taste. Summarizing objectively, if the game had more content and didn't rely so much on replaying the old levels, it would surely deserve a higher score.
Nevertheless, the self-mocking humour and obvious love that went into making of this game grant it the label of an overlooked gem. If you are looking for a fun and witty platformer, give I-Ninja a go.