I think the bad superhero flicks we've gotten is when they don't respect the spirit of the original comics. It's one thing to change up appearances, but you have to keep the spirit if you're doing anything about a hero that's higher than C or D list. Blade worked better because of how bad the original character was. Reading the old
Tomb of Dracula to where Blade debuted in is terrible. Blade seems like some throwaway character that was only created to have a token black guy. He got better during the 90s comics, and the movie took those changes and ran with it. That worked out great for a D list character like Blade, but it won't work with higher profile characters. Let's take the upcoming Green Lantern movie. They can alter his costume, when he meets his supporting cast, and even when he meets Abin Sur. But if they change the spirit of Green Lantern being about willpower and overcoming fear, then they've failed as an adaptation. Now it can end up being a good movie if they changed everything, but what's the point of making a movie based on a comic if you're going to change everything?
As for how good the movie is separate from the comics, I think alot of it has to do with not understanding how to tell a story. A great story is something that compels you, and it takes you through a journey. A crappy story is style over substance with too much CGI, and no quality in the script. If you want to make a good superhero movie you have to treat it like telling any other story. As the viewer I must be taken on a journey. There has to be a reason why I'm interested in the characters, and things have to make sense to some extent. When I say make sense I don't mean ultra realistic. Superheroes are called super for a reason.
What I mean is that the villain must have a real purpose, and the hero or heroine must have a valid reason to fight them. Wanted is a great example of what not to do in a movie. Things that are supposed to be cool happen for no reason at all. Why in the blue hell would he know how to shoot the wings off a fly, and how in the hell can he do that with no training at all? The filmmakers went for the crowd to ooh and ahh at the "cool moments," but if you take those away you have a truly terrible film. Batman Begins was really good in building up the need for a Batman. It didn't focus on Bruce Wayne doing cool moves, it focused on why he does what he does. The films must ultimately make sense.