1. Mega Man 3
2. SMB 3
3. Contra (or Super C can't decide)
4. Mike Tyson's Punch Out
5. Maniac Mansion
6. Castlevania
7. Mega Man 2
8. Bubble Bobble
9. Zelda II
10. TMNT

That was way harder than anything so meaningless should ever be. Also I recognize that there are better games than some of the ones on this list, but with the nostalgia factor kicked in these are probably the 10 I would be the saddest if I couldn't play again.