I will say the trailer exceeded my expectations of the film; I was expecting a complete mess, where as this trailer looks at least slightly promising.
Leto's Joker is the one aspect I'm completely sold on. I was cautiously optimistic when I saw the first photos, but his bit in the trailer dismissed any doubts I had.
Robbie's Harley Quinn I'm still iffy about. Her physical performance seems spot on, but her vocal performance seems lacking. And I'm still not a fan of her costume; Leto's Joker look, whether you love it or hate it, is a daring and creative new take on the character. Robbie's Harley is a lazier version of her look from the video games.
Smith's another one where he seems to have the physical part of the performance down but I'm skeptical about what he's going to bring to the role. Given that he had the second biggest showcase in the trailer after Harley and that his part did nothing to get me excited, I'm a little meh on him right now, and given Smith's quality as an actor, that's disappointing.
I rather liked Jai Courtney's little bit. Happen to be a fan of his back from Season 1 of Spartacus; haven't seen the Die Hard film he did or the new Terminator so I don't share the hate for him that's developing among a lot of movie goers.
Aside from them and Viola Davis who's perfectly cast, don't really have any opinions. I'm pretty much just going to see this movie based on Leto's Joker.