We know that the Avengers: Infinity War movies will focus on Thanos and his quest for godlike power, an idea pulled straight from The Infinity Gauntlet limited series. What parts of Gauntlet will the MCU use, and what parts are too weird or confusing to make it to the screen?
Although the announced Avengers movies carry the Infinity War title, they will almost certainly be based on the Infinity Gauntlet series by Jim Starlin. Infinity War (also by Starlin) was actually the sequel to Gauntlet, and is about evil doppelgangers from another dimension battling their counterparts in the Marvel Universe. All the teasers and Easter eggs in the Marvel movies point toward an overarching plot in which Thanos is collecting the Infinity Stones for some mysterious purpose, and that closely mirrors the events leading up to Infinity Gauntlet.
Of course, the movies aren't going to replicate the comic book series note for note, so let's figure out what they could use and what has to be jettisoned. Spoilers for early '90s comic book stories ahead.
Thanos' Motivation. In the comics, Thanos is literally in love with Death, not as a metaphysical concept, but as an actual being that embodies the cosmic force of death. Sometimes she appears as a skeleton in a purple cloak, sometimes as a 20-something brunette in a purple cloak. Thanos is red hot for her either way. His quest for infinite power is driven entirely by trying to make Death fall in love with him. They could keep this general idea for the movies, but I doubt we'll be seeing a woman walking around representing actual Death. There will be no romance angle, but Thanos as a worshipper of death makes him into a particularly creepy religious extremist. Which means we might also see his massive death shrine made of skulls.
Adam Warlock. Warlock is a key player in the Infinity Gauntlet, a being roughly equal in power to Thanos (Gauntlet aside). He manipulates events and acts as a general for the forces that fight against Thanos. He also ends up with the Gauntlet in the end. We've seen faint hints in the movies of Warlock's weird cocoon possibly appearing in the Collector's collection, so there's a chance Warlock shows up. But he has a bizarre and complicated history in the Marvel universe that seems like it would be tough to fit into a movie with a lot of other major characters already. It's possible he turns up in the next Guardians of the Galaxy movie, so he can show up in Avengers fully explained, but even so he's going to be very different from his comic book version.
The Infinity Watch. Adam Warlock pulls together a band of galactic misfits to help defeat Thanos. They're pretty vital to the overall story, but it's clear that the Guardians of the Galaxy will be positioned to take over this role. Gamora and Drax are Infinity Watch members, so putting them in the Guardians is a clear signal that we're headed in that direction. Rocket Raccoon is probably a better character than Pip the Troll in any case.
Mephisto. Throughout the series, the demon Mephisto hangs at Thanos' elbow like a sycophant, subtly manipulating the titan's emotions and decisions and eventually turning on him. It's pretty unlikely that one of the Marvel Universe's many Satan analogues is going to appear in the MCU, so I doubt we'll see Mephisto in this role. In fact, the role could be eliminated altogether (I can't imagine the movie having endless scenes of Thanos ranting on his space platform), although Loki would easily fit in here. I think there's a better place to use Loki, though.
Doctor Doom. In Gauntlet, Doctor Doom realizes what a terrifying threat Thanos poses to all existence, so he shows up to help the heroes. He's obviously also working to get his own hands on the Gauntlet, but it still makes for a solid villain/hero team-up. Rights issues are going to keep Doom far away from any Avengers movies (although I guess you can never say never). But MCU Loki would make a great substitute. The completely untrustworthy villain showing up to help creates all kinds of tension among the heroes and lots of great opportunities for blockbuster betrayals, and maybe even a bit of brotherly redemption.
Killing Half of the Universe. This is one of the things Thanos does to try and impress Death. He just decides that half of all people everywhere should be dead, and it happens. They just kind of vanish. It causes intergalactic wars to spring up, a bunch of heroes go missing, Silver Surfer gets totally freaked out, it's a bad scene. It's also perfect for an action movie — chaos and disaster and all kinds of things for the remaining heroes to fly around trying to solve.
The Cosmics. There's this whole squad of cosmic beings in the comic Marvel Universe that drift around in space and show up now and then to pass judgment or eat a planet or whatever. Most of them are anthropomorphized concepts like Eternity, Chaos, Order, Love, and Galactus. Plus the Living Tribunal. They all show up in Infinity Gauntlet and try to defeat Thanos. They will definitely not all show up in the movies. Unless the Guardians of the Galaxy movies get super, super weird, it's not going to happen. We might see them in a flashback or appearing in the background as a cool Easter egg, but they won't be major players in the story.
Zombie Nebula. When he has the Infinity Gauntlet, Thanos is essentially a deity. He thinks something and it happens. Nothing can harm him. So how does he lose the Gauntlet? Arrogance. He's taken his granddaughter Nebula and turned her into a semi-mindless shambling zombie form of herself, apparently just because he's a dick. So when Thanos is relaxing in his throne, Nebula strolls up and just yoinks the Gauntlet away from him, instantly restoring herself and draining all of Thanos' power. That's a pretty clutch scene, but the whole situation is pretty dark and gruesome. Nebula will probably turn up as Thanos' seemingly mindless slave, but probably not all desiccated and half-dead.
Spaaaaaaace. A lot of Infinity Gauntlet takes place in space. Part of the series' appeal are George Perez's excellent, Kirbyesque cosmic backdrops that underpin every scene. The MCU doesn't seem afraid to push things in weird, cosmic, magical directions; the Thor movies alone have established that. It would be pretty cool to see Iron Man and Captain Marvel zooming around battling against a background of swirling stellar nurseries!