#51 is notable as it serves as an epilogue to the preceding trilogy.
Reed Richards is researching other dimensions and is concerned that mankind is clearly not ready for threats such as Galactus. Sue asks if he (Galactus) will ever return and Reed replies "there's always a chance".
It was a sober moment as Reed realized that every foe the Fantastic Four had battled - including Mole Man, the Skrulls, Miracle Man, Sub-Mariner, Puppet Master, Impossible Man, Hulk, Red Ghost, Mad Thinker, Super-Skrull, Rama-Tut, Molecule Man, Hate Monger, Diablo, Invincible Man, Attuma, Gideon, Dragon Man, the Frightful Four and even Doom - were nothing next to Galactus.