Just got back to being able to play some Mutant Apocalypse, and it's definitely getting tougher. I restarted about half a dozen times on...
Plus that boss fight was a disaster until I learned how to cheese it. I've been gravitating toward Cyclops and Wolverine so far. I know you effectively have 10+ lives with all the characters combined but this game really needs some better balance. There are way to many situations with instant death or sections obviously designed for certain characters.
Overall though, I'm still liking it and the password system is a lifesaver.
EDIT:
Powered through the rest of Mutant Apocalypse. It was nails-hard and the difficulty feels like a result of poor, callous game design rather than a well-designed challenge. The amount of instant-death traps, trial-and-error boss fights, and the unsuitability of some characters for some situations with no option to change out mid-level (with a limited amount of lives for each) is very frustrating while playing.
On the other hand, you have the password system to allow for experimentation, and it feels like any character can technically make it through each level, even if some aren't as easy. Once you know about certain traps, you can avoid the instant-death scenarios fairly easily as well.
Once you get to that point, the game is still very tough (or it was to me at least), but it's also exciting and tense. The art is great and the soundtrack is at least pretty good. I'd give this game a 6/10 overall, but with a few changes it could easily be an 8.
Now onto lighter fare to close out the month, Castle of Illusion!