Awesome game, if you have a Sega Genesis, buy it!
So, I believe that for a review, you must judge it on several things (and so do most others, I think) : Story, Music, Graphics, Controls, Gameplay, Flow, Characters, Replay Value, Difficulty, Length, and Overall Quality.
Story: 8.5/10
The game starts out with an intro. It explains the whole story, about how there is a bunch of toxic sludge, so the humans build robots made out of orbs, called "Orbots", to clean up the mess while the humans are on another planet. But, while Vectorman is away, delivering sludge to the sun, a couple Orbots accidently attach a nuclear missle onto the leader of the Orbots, Raster. So Raster malfunctions and transforms into the evil WarHead, who "stands for tyranny, hatred, and oppression". He then controls the Orbots to turn the Earth into a total deathtrap for the humans. But, when Vectorman returns, he is unhindered by the mind control and starts his mission to go around Earth and destroy WarHead and his minions.
Music: 8/10
Pretty odd...but good. It seems to fit, and it's catchy, kinda techno-ish... hard to explain, really.
Graphics: 8.5/10
You can't really expect a whole lot from the SEGA Genesis graphicwise... but these graphics are good. Probably better than the SNES, in a lot of cases. The atmosphere is really something, and all the levels are unique. They're very clear, they're smooth, not pixely at all, except sometimes during explosions or something, they can get a little choppy... but then again, it's only a Genesis.
Controls: 10/10
I have to rate it perfect, because it's so simple! All you do is run, jump, and shoot.
Gameplay: 9.5/10
As just mentioned, it is really simple, yet highly addictive. You just run through the different levels, kill Orbots by shooting "Photons" out of his hand, and every now and then, find a power-up, such as health, lives, time, weapons, or transformations. Yes, Vectorman can transform. That's his signature move. He can be a bomb, a fish, jetpack, drill, etc. Plus, during certain levels, he's just one object throughout the whole level, such as a frog, tornado, or tank. His weapons are cool, too. He can have rapid-fire, a cannon, or shoot lasers that go right through enemies. And you might be lucky enough to find his most powerful attack, which only has one shot, but kills all enemies on the screen. In other words, gameplay is great and not repetitive at all, but can have it's faults.
Flow: 8.5/10
This just judges whether or not it's repetitive, glitchy, or at parts, boring. Well, it's definately isn't glitchy, not repetitive, but sometimes levels aren't nearly as good as others, but fun nonetheless.
Characters: 9.5/10
The only characters are Vectorman, WarHead, and the common enemies. Well, bosses too. Anyway, Vectorman is a neat character. He's kinda funny, too. WarHead is pretty cool, with nuclear missle and whatnot. And he makes a GREAT final boss. The enemies are neat, and very diverse. they all have different purposes. The bosses are all good, such as Clockwork, Sludge Barge, Aurora Borealis, and Acrobat. (You don't find out there names until after you beat the game with no cheats)
Replay Value: 8.5/10
It never gets old. 'Nuff said.
Difficulty: 10/10
A great challenge, and requires lots of practice. You definately get great bragging rights if you beat this game with no cheats.
Length: 9.5/10
Even though it only has 16 levels, they are all very unique and challenging. Sure, you could beat the game in a couple hours, but because you can't save, it will take much longer. Practice and patience are definately required for this game.
Overall Quality: 9/10
It is definately a great game, and I'd recommend it for anyone. But if you don't have a SEGA, it's available on the Wii Shop Channel, and I think the other 2 systems as well. (PS3 and XBox360)
So, hopefully this review helped.:)