Good question, but tough to answer...
1. Q*Bert (Arcade) - The first game I remember becoming obsessed with, and getting really good at. It’s still my favorite game ever.
2. TMNT (Arcade) - I played the hell out of this at the bowling alley while my parents were doing league bowling. Currently my second favorite game ever.
3. Super Mario Bros (NES) - It blew me away the first time someone showed it to me. It demonstrated the direction home video games were going, and prompted me to get an NES.
4. Final Fantasy II (IV) (SNES) - After I decided I hated Final Fantasy I on NES and that RPGs weren’t for me, I enjoyed this game so much it brought me back to the genre.
5. Street Fighter II (SNES) - The graphics and animation of the arcade version were mind-blowing at the time, and it became one of my most anticipated home console releases. It got me into the fighting game genre (not that I’m any good, I suck against other players, but I enjoy learning all the characters and beating the AI)