Since you like challenges, I think you'll have fun with this one. I hated it, but I didn't play it until well after I beat Super Metroid, which improved on literally every aspect of the original. The original was always considered a classic, though.
A. I also suggested Zelda 1, which he would probably need a walkthrough for, too.
B. He decided on Metroid, which I would imagine he would also need a walkthrough for
C. I can't compare it to the other NES Castlevanias because I have little to no experience with them.
D. I thought it was a fun game.
There's always Final Fantasy and the Dragon Warrior series. I didn't like Final Fantasy 1 but I didn't play it until after playing through the SNES ones. Never played any of the Dragon Warrior games, but from what I hear, they're supposed to be good.
Zelda 1 is my favorite video game of all time. EDIT: You'll probably need a walkthrough for it, though.
Couple more recs:
Double Dragon
Double Dragon 2
TMNT 2: The Arcade Game
ACTUALLY from 2015 to 2016 I took several coding classes at the local community college and the explanation made sense.
I was correct in that I didn't fully understand what the bug was about in the first place. I thought it was just about the computer time-stamping things, not users entering in dates into databases.