I loved Constantine and might watch it again one day (I rarely re-watch anything). It’s such a beautifully-shot film. And not surprisingly, at least part of the reason it looks so gorgeous is because it was shot on those unmatched Panavision Panaflex Platinum cameras with Panavision Primo lenses.
The video hints at it, but I think the reason the movie flopped is it does not hold your hand. It kicks you into the world and lets you sink or swim. Most sink because they want their thinking done for them. And Constantine is just not that kind of film.