Merely in terms of football? I like the Patriots/Ravens Divisional Game in 2014. Pats overcome two 14 point deficits, culminating in a wild finish and victory.
Way too much of this discussion has discussed the point scores and time remaining. What makes a game great are specific plays (or sequences of plays).
The Patriots/Ravens Divisional game had two extraordinary plays:
(1) The Edelman pass. Waiting 6 years to uncork a shocking play in an amazing scenario. All led up to with the perfect execution characteristic of the Pats: the many short passes/screens, and the famous Solder cut block.
(2) the ineligible receiver tactic. This to me is one of the most brilliant plays ever, because thousands of NFL games had been played, since the dawn of the league, and nobody had ever thought to use this idea in an NFL game, except one coach, in one game. That drive was capped by the Ravens coach getting an unsportsmanlike conduct penalty.
That game also had the Brady quarterback draw, which was nice to see.
SBLI had:
(1) the existence of this nearly unbroken streak of play after play after play, on offense and defense. That was the main thing.
(2) the Edelman catch, to me the greatest catch ever made. Not just a catch but a whole story, a play within a play, the twist being that the disadvantage - all the defenders around the ball - turned into an advantage - stopping the ball from hitting the ground. With the perfect double clutch to finish, and the trademark Belichick psychological domination causing Quinn to challenge.
(3) The blind passes, where Brady throws to a defender, without the receiver even looking at Brady, knowing that the receiver knows his route so will he will turn and get the pass. He did that to Hogan in a play that to my knowledge no other QB playing can even dream of executing.
SBXLIX had I think the greatest single play in NFL history. If you look at that in slow motion, it's eerie because everyone is standing still on the field but Butler is moving at normal speed, like an X-Men movie.
-------
So it's not just how much the comeback was by, it's how it was done: how amazing, how interesting.