The verdict: it's good, it's slightly confused by its own plot, and at times it is pure comic book awesomeness. Spiderman is the best Spiderman ever put on screen. I realise some hardcore Toby fans will call that heresy, but they nailed it. This Spiderman is perfect.
The whole civil war plot is pretty much an excuse for everyone to royal rumble, which is disappointing but also fine in some respects because the resulting action is some of the best in a Marvel film to date.
The true film is the (probably unintentional) years of repressed sexual tension between Tony and Steve exploding all over the place as they exchange emotional gazes and physical blows. Full spoilers:
Seriously, if Marvel aren't going to end phase 3 with them hooking up then they are painfully unaware of the bromantic subtext they've woven into these films. Tony, the flamboyant playboy who overcompensates with women in denial of his true feelings and recently dumped by Pepper, his first serious relationship; the Cap, a 100 year old virgin who spends half his time buffing up in the gym and prefers fighting with his buddies to asking out the girl he likes. When Tony sees Cap has a new BFF he goes for the throat and tries to punch him to death. Nobody's going to take his Steve away from him! But when Cap fights back he smashes Tony's arc reactor - a clear metaphor for breaking his heart.
Then he hand-writes Tony an actual apology letter. Could this be any clearer?!
Anyway, the civil war plot is confused. Not confusing, confused. It doesn't understand the point of itself. Both sides agree killing civilians is bad, mmkay, but disagree on whether they should be regulated and held accountable. They resolve this by battering the shit out of each other in an airport which luckily doesn't appear to have many innocents hanging around. At least none that they saw, so I guess it's fine and not at all the exact thing they all agreed they shouldn't do. But I don't mind this because this scene is superb. It's pure comic book glee, arguably surpassing the battle of New York in those terms. Spidey steals the show too, which is great.
Then Tony goes off on a vigilante mission and nonchalantly ignores his super mates being broken out of prison, because fuck accountability when it affects you and yours, right?
I maintain it's a good film, or at least a really enjoyable film, despite its internal idiocy. Well worth a watch.