Very good game once you put the time in.
X-Men 2: Clone Wars is all about classic 2D gameplay that is fast, smooth, and action-packed. There are seven X-Men to choose from, including the evil Magneto. All characters have a special ability, just like the first game; though in this game, the special attacks are unlimited. To make things even more interesting, your special ability gets stronger if you maintain a high amount of health. You'll also notice that the level of AI in the game is pretty high. Enemies will react to your attacks and will back up in self-defense. Some will even lead you with shots so that you will unintentionally run into a blast. Most of the time, the enemies won't kill you with brute force, but with tactics.
Graphically, Clone Wars destroys the first X-Men game. The character sprites are huge and smoothly animated, and there's a minimum of slowdown. Most of the levels are rich with detail, and push the Genesis to its limits - though there are a couple of levels that did have plain backgrounds.
As far as sound goes, this is one of the best sounding Genesis games I've ever heard! The music incorporates both the FM sound and digital samples to make some of the electronic rhythm sections. What's so remarkable about the sound is how CLEAN the digital samples sound. Sega Genesis isn't known for its crystal-clear audio, so it's very refreshing to hear it pull something off like this. Sound effects like explosions are FINALLY done right! Instead of cheesy "pop" sounds, the explosions actually have some oomph to them. Voice samples are a little disappointing though - they are limited to a bunch of "uhh!" sounds for when a character gets hurt.
If there's any problem I had with the game, it's the improper balancing in the characters. Take Wolverine, for example. He is not only the fastest character; but he can also climb on walls and ceilings, jump higher than most characters, AND he CAN REGENERATE! And therein lies the problem with the gameplay. Some of the X-men are so weak that picking them is to your disadvantage! And believe it or not, Magneto is one of the WEAKEST characters in the game. He's only useful in two stages throughout the entire game! The others - Cyclops, Gambit, and Beast - aren't really needed at all. So even though the game features seven X-men, only two of them will get regular use.
On the surface, it might not seem that Clone Wars packs a lot of replay value. After all, the ending is very weak - no big flashy finales in this game - only a static screen. But the true fun in this game is playing it over and over, trying to best your efficiency (going entire levels without getting hurt, etc). As you get better at the game, you'll start to notice that the game's controls are VERY tight and responsive, and that with a few quick-thinking moves, you can get yourself out of a very tight jam. I've been playing this game for twelve years (I'm 19), and every time I play it, I'm still wowed by its sheer quality.
I should mention that there's a two-player mode as well, but it's best left avoided. The framerate cuts in half when two players are playing, and the game suffers from camera trouble.
Even with its gameplay flaws, X-Men 2: Clone Wars is a fun, frenetic, and demanding platform game. It represents some of the best in 2D action gaming, and I personally wish that there were more games like it, in flashier packages (like Sega Saturn, or Dreamcast). If you can find it for a good price (like $5 or so), then don't hesitate to pick it up.