Incidentally, the difficulty of the NES original is highly exaggerated. The afternoon after I submitted this I broke it out for the first time since middle school and didn't even lose a life until the "find the blimp" stage.
The swimming level I remembered being so hard as a kid (and that people go on about like it's the hardest thing ever created) was a breeze.
The hard part was always getting to the last hall in the Technodrome with enough life and continues, because as a kid I never learned the trick to get by those jet pack guys without taking damage, so to have any chance you had to pretty much do a no-damage run up to that point, but notw that I know how t get by them even that isn't so bad. Being a hardcore speedrunner would still be tough because some of the glitches you'd need to use are beyond me but I feel like I could consistently run the game in 30 minutes if I spent a couple weeks practicing, and I'm pretty mediocre at games.
Even back in the day I found TMNT for NES easier than the NES Mario games, though and I've never really understood its reputation.