Legacy Making Game
I think this game will go a long way towards determining the legacy of Eli, Coughlin, and Brady and probably a few others.
Eli - If Eli gets his second Superbowl win it exponentially increases his chances of making the Hall of Fame. Only one quarterback has ever won 2 Superbowls and not made the HOF (Jim Plunkett, plus of course Brady and Roethlisberger who are still playing). If he wins, I think he needs maybe 3 more 4000 yard seasons to make it.
Coughlin - The list of coaches with 2 Superbowl wins not in the HOF is a bit longer (Tom Flores, Jimmy Johnson, and George Seifert are all 2-0 plus Parcells and Mike Shanahan are not yet eligible). However, I think with his 2 AFC Championship games with the Jaguars so soon after the team was founded, a second Superbowl win will put him over the top.
Brady - On the other side, if the Patriots win, Brady's 4-1 Superbowl record will give him a very strong case for best quarterback ever. But if the Giants win I think whenever someone says Brady is the best QB ever someone else will respond "But he lost 2 Superbowls to Eli Manning."