This is a really great topic and I've enjoyed reading all of it!
For as much as I love playing video games, I was never really amazing at them. I rarely am able to put myself "in the zone", so to speak, to the point where I'm just sort of operating above the game. It happens, but not consistently.
That said, here are a few games (including some that folks usually find challenging) that I used to play until I had some of them down to "auto-pilot":
Fester's Quest (NES)
Robocop (NES)
Mega Man (NES)
Spider-Man (Genesis)
Streets of Rage 2 & 3 (Genesis)
720° (NES)
Flicky (Genesis)
Goonies II (NES)
Karnov (NES)
Rygar (NES)
Aladdin (Genesis)
Mick & Mack (Genesis)
Sword of Sodan (Genesis)
The kicker is that I've gone back over the last 14 years or so and played these all again at various times... and I'm horrible at many of them. How I ever succeeded in Fester's Quest and Robocop is beyond me. Sword of Sodan is so difficult for me now, it's like it's broken.
The only explanation for this disparity in skill is what I imagine most of us experienced: as a kid, I almost never received new games and when I did, I played them to death, regardless of quality or difficulty; there simply weren't any more coming down the pipe anytime soon so I had no choice but to play them, ad nauseam. Same went for rentals: at best, I got to keep a rental for 3 days (Blockbuster). At worst, less than 24 hours (crappy mom & pop stores). When we rented games, my friends and I rarely set the controllers down until we either beat the game or developed a pounding headache and had to back away.
Nowadays, I have too many games and too short of an attention span to dedicate the precious minutes required to develop any long-lasting skill. Between work, home, goofin' in my studio, and myriad other hobbies and distractions, I play for a few hours at a time, at best, and I usually swap cartridges like a DJ swaps tracks. I get a quick fix, play until I'm pissed off and then move onto the next title. When it comes to video games, I wish I could say I still "got it" but the fact is that 12-year-old me would mop the floor with 33-year-old me all the live-long day, and twice on Sunday.
I still tear it up pretty good in SoR games, but I guess that's not saying much, compared to the others.