What's right/wrong with Constantine (2005) and what can we learn?

Constantine is not a terrible film, but it's very mixed. As it fits one of my favorite genres--urban fantasy, where magic is a small part of our real Earth--I think it's worthwhile looking at Constantine to see what it does right and what went wrong as a movie. There's probably more, but here's some loose thoughts. (And apologies for some of the cutesy names. I was looking at TV Tropes recently)

Right:

• Some of the exposition/background occurs in dialogue that overlaps with some plot-related moment
• Salvation by suicide: turning a lot of what we expect around, the movie delivers an ending where Satan saves the day and John's embrace of suicide turns out to be OK--since it was for right reasons--it's theologically shaky, but a good surprise/repay of the opening
• Casting: Peter Stormare makes an engaging and creepy Satan and Tilda Swinton should be in all the movies

Wrong:

• Much of the exposition/background is given with dialogue that is pretty bland or outright campy (as when Angela pushes aside info on "the Spear of Destiny" with "I know, I'm Catholic")
• Opening title card tells us, as boringly as possible, some backstory on that Spear: blah blah, lost since WWII--but how much cooler it would have been if some guy just found this old spear wrapped in a Nazi flag and we had that mystery about what it was rather than that answer?
• Too cool as a rule: there's a thin line between being a jaded demon-fighter and having the dry cool wit of an action hero (as the Simpsons parody of that style goes)--and John Constantine mostly comes off as a rote action hero
• A Q for every hero: So much of the battles here are purely super-weapon vs. demon, which decreases suspense--so that many of the battle scenes have no emotional tension (not even the suspense of "how will he get out of this?"--we know how he'll get out of this, we've seen the flamethrower)
• Scene without tension: when John faces a room full of half-demons, one of them helpfully says "Holy water" before they all start burning and then Constantine starts shooting, which looks OK, but has no emotional weight
• Repetition: Characters occasionally tell each other things that we the audience already know; once, John uses a magic means to watch the prologue of the movie that we already saw--which is important for him to know, but boring for us to watch
• Didn't we see that already?: In a climactic scene, two guys join forces to exorcise a woman. Sure, lots of exorcisms look the same, but why invite the comparison with The Exorcist?
• That final message from Constantine about god having a plan; and that post-credit scene where Chas is/was a half-angel--both overwrought
• Casting: Keanu Reeves does a nice "Zen blankness" (as one critic noted), but isn't quite right for the jerkiness of this character
• Occult inconsistency: We're told that God and Lucifer aren't allowed on Earth, but half-breeds can intervene, so then what is Tilda Swinton's Gabriel and Gavin Rossdale's Balthazar? And the end, when Satan shows up?
• Character motivation hard to connect to: Constantine has a clear, but odd goal: as a suicide, he's doomed to go to Hell, so he tries to please God by sending demons to Hell... which means that Hell would be full of people who hate him. Given that Constantine can be part of the battle, if his motivation is pure self-interest, why isn't he fighting for Satan, so that his arrival in Hell would be a home-coming? And while the movie has a fine arc for John of self-interest (get me to Heaven) to other-interest (save Angela and her twin sister), I feel like they try to get our interest in him by making him cool rather than making him human/identifiable.
• Do we need him here?: Constantine's ally Chas disappears for a good chunk of the movie. So why is he here--along with Constantine's other allies, Angela, Beeman, Hennessy, Midnite? (Alt question: who isn't on Constantine's side?)
• Sudden but inevitable betrayal: we hear that Mammon needs Godly help to get to Earth, which is one piece that sets up Gabriel's heel-turn (or reveal as a villain if you don't like wrestling lingo). But there's no real heft to that betrayal/position?

So, overall, I think Constantine's problems really have to do with the delivery of information about this strange world--it's at its best when it can dramatize that info; and with the strangeness of characters within that milieu (i.e., what does John Constantine want?).