Developer Crystal Dynamics gave the world its first glimpse at Marvel's Avengers during the Square Enix E3 press conference, and while a lot remains to be revealed, there were a ton of details touched on. And prior to the official E3 reveal, rumors suggested that the Marvel's Avengers would have 4-player co-op and customization, which were both confirmed at the showcase.
The latter came to the fore when it was revealed that Marvel's Avengers is a loot-based game that features gear customization. It's not fully explained, but it seems as if players can build their own unique and "ideal version of Earth's Mightiest Heroes" by collecting gear and unlocking skills. It is also boasted that there are "nearly limitless ways" to customize the heroes in the game through this gear customization system.
This leaves a lot to the imagination and obtains prompts unanswered questions such as how many gear slots there are, if gear is related to cosmetics, if there are character-unique gear slots, if that means multiple people can play their unique versions of the same character at the same time, and how it all ties into the skills. These questions would likely be answered prior to the launch of Marvel's Avengers in May 2020, however.
It seems the Marvel game will feature original, fan-favorite, and classic cosmetic outfits, which may or may not tie into the loot and gear customization. Considering the free DLC plans for Marvel's Avengers, though, it's safe to say these items will not be locked behind loot boxes or have a pay-to-win aspect. Even though the gameplay is not competitive multiplayer, simply paying for cosmetics that make someone stronger would not likely get a swell reception.
Speaking of the characters, it was also revealed that Marvel's Avengers will feature an expanding cast of playable characters, though it will begin with the core 5 (Captain America, Iron Man, Thor, Hulk, and Black Widow). Hank Pym's Ant-Man was set-up as one of the first additions to the game, but many more will likely come post-launch.
Marvel's Avengers releases May 15, 2020, for Google Stadia, PC, PS4, and Xbox One.