This was another one of those games that kept people coming back to arcades back in the day. You really couldn't get the same experience at home, and watching those transformation screens of your guy turning into a golden werewolf was awesome. The Genesis home version of this game is a semi-decent translation but leaves a little to be desired.
For anyone who's never played the original turn off your browser and fire up MAME because you're missing one of the best 16 bit games of all time. It's a take on the usual side scrolling beat'em up with the twist being you can "power-up" by collecting these floating spirit balls, eventually turning into a different super-powered altered beast for each level.
For the most part it's a pretty faithful port of the arcade game. All of the levels and gameplay elements are there. One of the cool things about this game were the multiple enemy types that would come at you, slow moving, shambling zombies, horned half-decayed demon things, two headed wolves, limbless bouncing frogs, strange weird half-chicken lizard monsters, etc. Each one has it's own unique animation and design, although most of them attack you by merely running into you. You counter attack by punching and kicking, and after your animalistic transformation you get various powers depending on which level you're on (these usually include some sort of projectile and body attack.)
At the end of each level you face the sorcerer Neff in any one of his incarnations. These confrontations are the essence of what any good boss battle should be - a large and powerful opponent that attacks in it's own unique way in which you must quickly figure out and exploit it's weak spot. Some of these boss monsters are just straight up bizarre - level one has you facing a demon made up of rotting bodies who throws multiples of his own head at you, level two is this strange watermelon plant made up of eyes, etc.
Weak points: The game is too slow. The screen autoscrolls very slowly, which forces you to fight all of the various demons and things whereas in any other game you could avoid them. The spirit balls are only available from a shining two headed wolf that sometimes appears at the most inopportune times - miss the wolf and you get no powerup. If you die and continue during a boss battle then you have to face him as a skinny human, which makes the fight extremely long.
Overall the game remains a classic with good gameplay, great character design, and quintessential boss battles. This is one of the arcade classics that made Sega great.
Graphics: Genesis graphics aren't quite up to par with the arcade version. The characters are slightly smaller, and there is some break up in explosions (for example, when the 2nd level watermelon-eyeball boss dies the resulting explosion looks pretty ghetto.) In the arcade version when you killed a monster it's body parts would scale out like it's flying at the screen. Sadly the Genesis couldn't handle that and settled for the monsters dissolving into flaming spherical balls, which looks kind of strange. For the most part only anal-arcade people will even notice these changes though.
Sound: Very accurate samples (although they are noticeably downgraded.) For some reason all background music has to stop when you get a spirit ball and the "Power up!" voice clip plays, which is annoying.
Gameplay: Slow but never tedious. Each enemy dies after a few hits and the fun lies in finding the right position and attack to use. Once you transform it's usually a slaughter until the end bosses, which take a little forethought to destroy but aren't too hard.