Mario is Missing! for the NES and Super Mario Bros. for the NES
Played both on the same day as a kid, and I liked Mario is Missing! more (I have no idea why).
I really liked the music in Mario is Missing! as a kid, and in a classic kids fashion I didn't read anything and just mashed buttons until it worked. It's not a big surprise that I didn't finish the first room/town of the game until recently when I was able to find a copy.
As for Super Mario Bros. I played that game a bunch but I didn't like it due to how difficult it was, as well as having stiff controls just added to the anger. Probably disliked it because I could die and lose progress in it, which isn't present in Mario is Missing!.
Sonic The Hedgehog 2 for the Genesis
Played it at a friends house when I was a bit older, it's a fun game.
Not my type of game, but it's a fun game.
I distinctly remember how my friend was always surprised at how good I was at it, even though I just hold right and win.
The first act boss was a bit tricky the first time, but it wasn't anything major to talk about.
Overall, as I said before, fun game.
Lots of love, S1Z2