Incredibly...NO....Maddeningly...NO....RIDICULOUSLY HARD!!! Easily in my top 5 list of hardest games to beat.
On to Wolverine's level. You're in some kind of carnival themed house with jack in the box enemies armed with machine guns. The benefit of playing as Wolvie is that if you sheath your claws and remain still, you regenerate health (oh how you'll need it). Too bad it takes forever and a day to regenerate your health. You encounter Apocalypse in the first boss battle in which he jumps all over the place and is very difficult to get past but it's not nearly as bad as some of the areas. The final section boss battle is with Juggernaut where you have to cut through ropes that hold anvils, dropping the anvils onto Juggernaut as he runs at you. This also is incredibly tough and takes forever.
Cyclops is in the mines. The hardest part of his level is that there's areas where you need to jump but you can't see what's below you. This makes it impossible to know exactly where you should jump to and more than likely you'll end up on the electrified tracks.
Storm is in a giant water-filled area and you need to break water valves to release water so that you can float up to the surface. The catch? You have to break them in a specific order (not specified at all) so that the water rises little by little. Break the wrong valve and you can end up drowning yourself. Now my favorite level (that's completely sarcastic). Gambit's level. This area starts with a giant spiked ball rolling after you that takes up the entire hight of the screen. You need to move as fast as you can to the right while jumping over stuff, destroying blocking barriers, and enemies. What makes this level ridiculously tough is that the number of cards you have is limited and the only way to gain more is to destroy an enemy and pick up cards from them, or find stashes of them. I don't know how many times I've gotten 3/4 of the way through the level and got stuck by blocks that I couldn't destroy b/c I ran out of cards. I strongly suggest you tackle this level first b/c chances are this is going to be the one that gets you every time.
I have beaten this game one time. One time in all the years I've played it. I still own it for SNES and pop it in once in a while to remind myself what a hard game plays like. This is harder than TMNT 1 for NES. This is just as hard if not harder than Battletoads for NES. There are no game saves or passwords or continues in this game. You have a few lives for each character and that's it. For those of you looking for a challenge, this is it. Go on, try it. See if you can beat it. I dare you. To those of you up to the challenge, good luck! You'll need it.