SB 42 wasn't the greatest game ever. It was a really good game with a signature play, and obviously its significance was huge in keeping NE from 19-0. But in terms of the excitement level and quality of the game, it pales in comparison to SB 49 (which I think should have been #1 on the list).
SB 49 had a team at the peak of its power, a budding dynasty, the defending champion with an all-time great defense in Seattle, against Brady, Belichick, and the resurgent Patriots trying for their first SB title since the 2004 season (none since Spygate). There was a controversy brewing (Deflategate). It was back-and-forth, haymakers thrown by both teams. It featured great defense and also great offense. It also was, til that point in time, the biggest comeback ever in a SB. And it also featured the greatest single play of all time. Moreover, it denied Seattle dynasty status and gave Brady title #4, tying him with Montana and Bradshaw. And it launched the second Pats' dynasty.
It had everything - excitement, drama, amazing plays, superduperstars, elite coaches, the works. SB 49 was the greatest game ever.