Ghost Rider vs Galactus is interesting, I like the idea of an eldritch battle between supernatural horror and cosmic horror.
The Rocket Racoon & Doctor Doom will probably be a good time with what sounds like super geniuses in an Odd Couple setup.
My only confusion is the Spider-Man vs Doc Ock issue. No matter what way I look at it, Spider-Man fighting one of his most iconic villains doesn't feel like it fits in this series about unlikely duos.
Also Hulk and Doctor Strange aren't really an unlikely duo - they were both founding members of the Defenders, along with Namor and the Silver Surfer. Hulk and Strange are also both affiliated with the Avengers.