Publisher: Sega
Developer: Sega
Size: 2 megs
No. of players: 1
Got it for: $4.90, cart only.
Apparently, an evil force has put a spell on the Rainbow Ninja Organization(the RNO), forcing them to do evil deeds. One ninja, Mr. Red Ninja, has either broken the spell...or was never put under the spell, or pretended to be under the spell so he could finally have a good excuse for constantly stealing children's lunch money, whatever. At any rate, he heads out to free his brother ninjas from the evil force...

What's it all about?
It's a mix of every 2D, sidescrolling Shinobi game out there. Using various elements from each game you move through one of the five stages(each with multiple levels within) in an attempt to free a ninja that has been captured. After freeing a ninja, you are then able to switch to that ninja from there on out. Each ninja has a different weapon, slightly different abilities and a completely different ninja magic. Knowing which ninja to use in a certain situation is mandatory, and once you get used to their specifics, it's pretty easy to figure out which one would be the best for the task at hand. After freeing all the ninjas, you move onto the final level where all of the ninjas' abilities are put to a final test as you make your way closer to the final evil...
Graphics - Amazing...just amazing. From the multiple parallax levels of the Highway, to rapids and special effects of the caves in the Valley, and everything in between, the graphics will just knock you back. It isn't just "great...for the Game Gear", this is all-out great no matter how you cut it. The ninjas, and the enemies all look nice as well, with a decent amount of animation and detail going for them. Bosses are, in true Shinobi fashion, over the top in terms of either size or playing field...it's really something to see.
Sound - Though its definitely got that "8-bit" quality thing going for it, the sound is just excellent. The music has some amazing quality to it and the tunes are just killer; mix that in with the various Revenge of Shinobi pieces and you've got a bad-ass soundtrack. The sound effects also rock, with the various explosions, sword swipes and other effects.
Control - Solid. The ninjas don't move all that fast(which is kinda weird figuring that they're ninjas and all), but you get used to the pace really quickly, and the smooth control really helps out in that. There's no delay to any of the various actions they can perform, including breaking out the ninja magic.
AI - A lot of enemies tend to run in their pre-set patterns, but there are those that will actively come after you. There are a few cheap hits in the fray, with enemies jumping out and hitting you almost instantaneously, but it only really happens on one specific level(the Valley), so it's easily forgivable. Other than that, the AI is very fair, which adds to the fun of the game.
Replay value - As I've said before: It's a cross between every Shinobi game you've ever played...so what do you think? Hell yeah you'll play it again....and again, and again, and again, and again. The levels are relatively short, but are really fun to go through, especially messing around with the order you take them in and ninjas you have with you.
Tips for better gaming experiences:
Though you can go through the levels in whichever order you want, the easiest route(and the one that allows you to pick up each and every health extender) is as follows: Highway, Valley, Harbor and then Woodland. Also, for more, in-depth help be sure to check out Devin Lamb's excellent GG Shinobi FAQ!
Game Genie:
If you're having trouble in the game, the following two codes have you covered:

21F 055 2A2 - Infinite energy
006 06D 3BE - Infinite lives  
Click above for more GG codes

My rating: 90(out of 100) - A rock solid game for the Game Gear, something that should be in *every* owner's collection. Excellent gameplay, amazing graphics and rockin' sound will have you wishing the game was just a bit longer...but then again, it'll also have you really appreciating every single minute you get with this remarkable Game Gear title.
GamePro gave it: 5.0(graphics), 5.0(sound), 5.0(gameplay), 5.0(funfactor), 4.0(challenge)(out of 5)

Cat's review: I don't know what it is....I just can't keep pawing at the screen. The little shinobis look so tasty...so cute....
I'm sure they don't mind ninjas jumping on their cars.
A little ninja magic with Red.
Another Shinobi-signature boss battle.
Tearing it up at the docks with Pink...
Hitting the rapids with Yellow.
Yeehaw, swinging Blue ninja!
Keeping it real...real Shinobi:
GG Shinobi borrows more than just a bit from its predecessors, which is a good thing...it even uses music from the excellent Revenge of Shinobi soundtrack by Yuzo Koshiro! To listen through the various cuts, hold Up and Button 2 at the title screen, then press Start. Rock on...