Sonic 3 & Knuckles and it's been my favorite for over 20 years.

Aside from general nostalgia I tend to rate games on how frequently I can play them without tiring and this one I can play all the time. Many people consider it or Sonic 2 to be the best in the series, but it was always been more special than just a "best of show" game for me and I don't even really know why.

The Genesis Sonic games in general are great to fall back on. Especially after a bad day they can just kind of take me away from things for a bit.

Now ask what my most important game of all time is and you'll get a completely different answer.