The first thing that pops to mind is the Turbo Tunnel level.
That’s obvious and the author of the post remembers it vividly. That seems to be as far as the author ever got. His entire post is based on that level. I memorized my way through it all and I could probably still find the warp.
I can’t recall a single level after that point that was easy. This game broke even the most battle-hardened players. The only way I got through it was with a Game Genie. I wasn’t proud of it, but I had no idea how the ending played out and there weren’t any YouTube walkthroughs to watch when I was 10.
And playing with someone else? Forget it. It was better to just beat the shit out of each other all afternoon instead of trying to tackle any level past 2.