This be "Da bomb!" Kaboom, it is the bomb sir, yes.
After you get other upgrades by going to the gym, sword mechanic, etc, the bosses will get progressively harder. You have sidejobs available as well, which help you earn money to pay the fee to fight a boss, and therefore go up one rank in the United Assassins Association. Further in the game, you get more jobs available that pay you more DINERO! The highest paying job being an assassin mission where you have three minutes to kill as many thugs as you can and get a lot of DINERO for each kill. My record is 98 kills! I would have gotten my goal of 100 but the game pauses everything in place as soon as the time runs out and doesn't count the people that are half sliced and half a second away from counting as FINISSSHHED! This job helps you easily get $100,000+ and it gets really easy to go from boss to boss and pass the game after the 4th rank battle. I spent a lot of time playing mostly trying to get gold medals in all of the sidejobs and assassin missions.
It was unfortunate that there wasn't too much tension built up before fighting the rank bosses. You couldn't really feel like you were immersed in each level(not including the boss fights) as the game would just throw a cockroach-load of simple enemies at you, that could easily be disposed of in a couple of swings of the Wiimote.
The game had funny cutscenes and you get some nice upgrades and accessories, like a selection of 100 DIFFERENT TYPES OF SHIRTS AND PANTS AND JACKETS(only 30 available before you pass the game).
The game had a great final ending secret battle. It is unlocked if you have bought all five beam katanas.