A lot of writers don't really know what to do with Ant-Man. Several times over the character's history, his role in stories has been reduced to the ol' "shrink down and go inside someone's body to cure them of an illness" trope. You've seen this bit in everything from movies like Fantastic Voyage and Innerspace to farcical cartoons like Family Guy and Archer. It's not really impressive to see a dude in spandex plumb someone's bowels -- even if that someone is the Hulk.
A creative exception came early on in Ant-Man's career (when Hank Pym still used the name), when in Avengers #93, Vision collapsed due to a mysterious android illness. This was clearly a job for the guy who can shrink down to the size of a molecule. As you might imagine, the innards of a robot are just a tad different than a human.
The trippy Neal Adams visuals are a sight to behold. Instead of familiar red blood cells and veiny passageways, Vision's insides look like a funhouse on an alien planet that was taken over by machines who run on acid.
Ant-Man eventually figures out the problem and fixes some loose wiring in Vision's brain. He ends up emerging from Vision's mouth, right next to his baffling robot uvula.
If Ant-Man ends up being a big part of the Marvel Cinematic Universe, it could be a lot of fun seeing this kind of thing unfold with an insane special effects budget. For now, you might want to refrain from Googling "Paul Rudd inside Paul Bettany."
Marvel movies probably need some ramp-up for this, but it's inevitable. If Ant-Man can shrink, he has to be able to grow up back to normal size. If he can grow, he should logically be able to grow to a size larger than an average human. And in the case of Giant Man, "larger than the average human" can mean "as tall as Godzilla." Hank Pym has used Pym Particles in this manner tons of times, like when he fought C-tier supervillain and double-ply paper towel spokesman Absorbing Man.
Annihilating city blocks with wanton superhero destruction has been out of style since Man of Steel, but this kind of kaiju-level brawl would look awesome on the big screen. It'd be like Pacific Rim, only instead of giant mechs picking up buildings and chucking them at each other, it'd be two sweaty guys.
Of course, the downside of this comes when and if we ever get to cinematic Marvel Zombies...
Let's hope we never get that far.