Just my 2 cents.
Reptile:
Never been much of a Reptile fan, but I'm loving his design this game, and think that of all the characters shown yet, he looks the best comparatively speaking. Not much else to say other than they really knocked it out of the park with his design, and I like seeing Baraka and Reptile on the good guys' team this time around. Kinda got me looking forward to the story.
Havik:
Very excited to have Havik back, though I do have some nitpicks that will hopefully be resolved with other costumes. First and foremost, I wish he looked more skeleton-like in the face instead of what his lower face looks like now (maybe mangled is the word?). Also, even though I like his costume, I hope we have others that are more cleric-like since he's supposed to be a Cleric of Chaos. Other than that, love what I see, and the moment he ripped his arm off and used it as a weapon, I was sold. One of the characters I'm looking forward to trying out the most right now.
Ashrah:
Of the revealed 3, she was the character I was most hyped about, which is likely why I'm the least impressed with her. I knew I would be since there's been so much amazing fan art of Ashrah over the years (even in the new movie she looks great), and I had a feeling the game wouldn't stack up to it. Just like with Havik, I'm hoping she has some alts that I like more. I'm baffled by the decision not to have her iconic hat in her debut trailer/default outfit. Like others have said, she kind of looks like D'Vorah with human skin. For me, compared to a lot of the 10/10 fanart I've seen of her, I'm quite let down, but I'm holding out hope that there are some good alternates.
Sareena:
Thrilled to have Sareena back. I was actually so excited to see Havik, I didn't notice her at first, and was very confused as to who she was when in demon form. The only thing I really have to say is that I think her demon form is really uninspired. It really just looks like a generic devil, and I gotta say I think it's pretty low-effort. I'm happy to have her back, but considering how her demon form looks, I would have preferred we just see her human form only instead during battle.
Overall, I'm happy with what I see, and with some good alternative costumes, I think all of the characters shown are main-worthy for me.