That would depend on who you ask. I've been reading comic for 50 years, so my "drastic" might be different than someone who's been reading them for 10 or 20 years. The Guardians for example look nothing like my memories of the characters because they've changed alot since I last cared about those characters. Heck to me Vance Astro and his pals are the Guardians, not Starlord and his pals. But I loved the movie.Nothing terribly drastic. Spider-Man, The Guardians, the Avengers, nothing at all is even close to as drastic as characters like Aquaman, Superman, and the Joker. Heck, unless you told someone who didn't know that the picture of Mamoa's Aquaman WAS Aquaman, there's zero chance they'd guess that based only on the information in the picture. For example.
Though Batman is looking great from what we've seen so far. More so than almost all other live adaptations.
And why isn't Thor lame Doctor Don Blake? Where are the Stone Men from Saturn? Bucky's supposed to be a kid! No Ant Man and the Wasp? That's not the Avengers!!!! Tony's personality is all wrong!!!! He's not that much of dick!!! Hawkeye isn't an Agent of SHIELD! Why isn't he more of a dick? Black Widow was a villain back then! Where's the Mansion and Jarvis?
To most people Aquaman is the underwater guy who talks to fish. As long as Momoa's version includes something along those lines, I doubt people will care.