There's a lot of actors these days who take their craft very, VERY seriously -- refusing to break character while on set ... a technique Mads Mikkelsen is calling absolutely absurd.

The Danish actor -- who most recently replaced Johnny Depp in 'Fantastic Beasts,' and who has a crap ton of other credits over the years -- let his honest opinions on method acting fly in an interview with GQ UK ... saying getting that into character for a role is "bull****."

In his sit-down with the mag, they say he was made aware of Lady Gaga reportedly continuing to act as Patrizia Reggiani in 'House of Gucci,' even when cameras weren't rolling. Ditto for 'Succession' star Jeremy Strong -- who's been reported to have taken things to uncomfortable extremes on different productions of his.

All the same ... Mads says he isn't impressed with the so-called commitment. While he does acknowledge he appropriately prepares for roles -- including learning a skill he might need to exhibit on camera -- he notes ... "But preparation, you can take into insanity."

He adds, "What if it’s a s*** film -- what do you think you achieved? Am I impressed that you didn’t drop character? You should have dropped it from the beginning! How do you prepare for a serial killer? You gonna spend two years checking it out?"

Mads essentially makes this distinction ... you're either a great actor, or you aren't -- and he believes that while Daniel Day-Lewis (the king of method) has, perhaps, pretentiously taken things too far in the past ... he also thinks the dude's just inherently fantastic at what he does, which is why it works. Not so much for the actual deep devotion to a role itself.

Of course, more and more actors are all in on method lately -- especially Jared Leto, who infamously stayed in character for a number of roles ... including when he starred as the Joker in 'Suicide Squad,' for which he reportedly caught flak from castmates and crew.

Even as recently as his shoot on 'Morbius' -- a character depicted as a disabled doctor-turned-superhero who can't walk properly -- Leto is reported to have stayed in character by using crutches everywhere on set. But when time was of the essence and he had to whizz ... the guy apparently hopped into a wheelchair and rolled himself to the John.

Indeed, it seems Mads' point here is ... you can do all the character-y stuff you want -- but a good actor, perhaps, doesn't necessarily have endure what their character does to churn out a good performance.