Hellboy in the 2019 film is supposed to be more emotional, darker, and grittier than in the original films. The character is also portrayed as younger. David Harbour’s Hellboy is supposed to have the mentality more of a teenager than a mature man and he is trying to decide whether he is truly a good person despite being a cambion. The makeup design is also supposed to be more realistic and biologically believable but at the same time more infernal. The creatures from Hell, including Hellboy, are supposed to be very different from terrestrial life-forms and more disturbing. They are from Hell after all. The makers of the new film also want to mix in elements both of comic book cannon and of horror.
Furthermore, they do not want to make it another origin story because they believe that Del Toro did very will in that. Instead, they are expanding the Hellboy universe. One thing that can be said is that it will be different, but whether David Harbour’s Hellboy will be better than Ron Perlman’s is primarily a matter of taste.