When one looks through the history of 16-bit video games, they will notice the unbelieveable number of comic-licensed side scrolling beat 'em ups (Spider-Man, Batman, Spawn, and the X-Men among others; funny because most of them were from Acclaim), most of which all played the same and really didn't offer much in the terms of fun and replayability.  Sega's original X-Men game was an exception that captured some of the intensity of the comic and Fox cartoon, and its' sequel X-Men 2: The Clone Wars also excells above most of the other comic licensed games.  You can choose to play as Beast, Cyclops, Gambit, Nightcrawler, Psylocke, and Wolverine, and after defeating Magneto on Asteroid M you get to play as him as well (and he is the best character in the game).  The levels are huge and expansive and include Siberia, Asteroid M, the Amazon jungle, and the Phalanx clone laboritories.  The bosses are tough and range from Apocalypse, Brainchild, Tusk, a Sentinel brain, clones of the X-Men, and the huge rampaging Brood beast that chases after you in the final level.  The characters are nicely animated and are large,  pixelated, and colorful and resemble they're comic counterparts.  The control scheme is simple, and the background music is actually great (and that is saying something considering the Genesis didn't have the best sound chip in the world) and the difficulty will make you come back and play it again and again.  All in all, if you still have your Genesis and are an X-Men fan then find this game quick, or if you still have this hold on to it.