Omega Vision
Face Flowed Into Her Eyes
If I were the writer:
Thor-Retool of the character, maybe. Give him a beard (not necessarily a large one) and make him speak in in heavily accented English with little bits of Old Norse phraseology (curse words, nick-names, "slang"😉. Also have Mjolnir decorated with glowing Norse Runes, the same for his body armor. His power-level is fine where it is now.
Silver Surfer-I don't read a lot of Surfer and don't know much about his character. I'd say he's fine where he is though.
Superman-Remove the magic weakness or give him some magic resistance, make him use speed more often to win fights, give him some more complex motivations for doing what he does but don't make him any 'meaner' or more willing to kill just because that's what the Lowest Common Denominator of comics fans wishes it so. That said I would also avoid having him kill sentient robots or such and such just because they aren't organic.
Hulk-Make Banner Hulk again and put his powers back at Savage levels but still give him something of a mind, a mind that is nonetheless made muddled by the contest between the Id (Hulk) and the Superego (Banner), a contest that would be shown by competing captions expressing his conflicting desires and intents.
Thanos-Have him break up with Death and after being cast out of her Realm make his story the search for purpose and identity.
Darkseid-No more jobbing, restore him to PC levels and make him a threat to the entire DCU, a threat that the combined JLA and JSA struggle with. Also make him more of a planner and manipulator and less a petty tyrant. Now that Kirby's original story has more or less been closed up by Morrison I'd have a revived Darkseid quest for something else than the Anti-Life Equation: his freedom. I'd have Darkseid come to the understanding that he is just a pawn of some Cosmic game and attempt to break free and snap the strings. He'd soon realize that the only way he could ever possibly break free of the cycle would be to undo Creation itself: the Source. At the end of his story he'd realize to his devastation that in seeking to free himself from Fate's grasp he played right into the Cosmic design and secured his own end.
Wolverine-Restrict him to one team and two solo series maximum.
Spiderman-Retcon OMD/BND
Deathstroke-Make him an anti-hero again who's sick of his Supervillain lifestyle and who's trying his best to make up for some of the wrongs he's done.
Sentry-Lose the Void/Bob dynamic and exile him from Earth completely. Eventually have him join the Marvel cosmic order as a Galactus level being, maybe even make him Marvel's Spectre.