One word: Frustration!
Again, this game is brutal. If you don't like old-school games then by all means stay away from this one. This is for the best of the best in retro-gaming and is extremely unforgiving. I was actually impressed with how many creative ways they used the 2D platforming to insinuate your death, such as Airplane exit doors opening in mid-flight creating a vacuum to suck you out. Part of the frustration comes from when you are hit by an enemy projectile. Not only are you thrown back, but you become immobile for several seconds. resulting in a terrible twist of fate. A second frustration is the inconsistency of enemies' patterns. Timing and rhythm do play a factor in it. But the enemy is so adaptable to your movements that I could never figure it out. Almost every little move you make will depend how the enemy will respond.
The boss battles created a very mixed reaction in me. While some of the bosses are completely awesome (as a ninja you get to kick Spider-man, Batman, Rambo, Godzilla, and the Terminator's butt), other boss battles were extremely tedious and even, dare I say, boring.
This isn't the best looking Sega Genesis games, but for it's time back in 1989, Revenge of Shinobi was pure eye candy. It does have a destinct art style to it, which would definitely appeal to the fans of the 80's and early 90's and relatively speak it is a good-looking game. Joe Musashi is rather stiff for a ninja, though. I love how he floats when he jumps like something straight out of Crouching Tiger, Hidden Dragon.
As I've mentioned in my blog, I have a very high respect for Yuzo Koshiro's works as a composer and Revenge of Shinobi is no exception. This game sounds great. While the majority of it is electronica it still maintains a oriental flavor, which I absolutely love.
In closing, Revenge of Shinobi is an game that is easily recommended to the hard-core fans of the 16-bit generation, while those with anger management problems should probably look some where else.