I may be a bit opposite of what some are saying. So please, just hear my little rant. DC in my opinion as far as movies go can not be fully what the characters were originally. Marvel has made their movies bright, flashy, large scale, and they did it well with a lot of action. DC has started a good line with Chris Nolan in several ways, if more movie makers for other DC movies and the JLA would follow them. TDK is dark and it is gritty and edgy. However, it has deep meaning in the story. The story goes somewhere. And you can tell by the previews of TDK Rises that there is light in some way at the end of the story and although Batman is edgy and dark his values have still shown through.
Now translate Nolan's realistic style of filming and story over to the super powered heroes of DC. How do you make superman more real and relateable. One way I guess is to dumb down his powers just a bit so he does feel pain. Doesn't kill him but he feels pain.
My view is hard to explain. I can visualize it, but it's hard to convey. Create a large story that is deep, and emotional. That's where DC can go that Marvel hasn't so much. They have big action and large scenes. DC can be dark, but it can be full of emotion. A serious take on the super heroes and their lives.
Bring them together in some way that unites them in a serious story full of emotion, struggle and even heartache. Heck, for some of the lesser characters like in Marvel, throw 2-3 together as though they have been trying to come together and do what no one has. Have one of them sacrific and die to unite the rest? Far out, but just brainstorming.
Superman and Batman don't need reboots to do the JLA. Other characters need to be done first though. WW, Flash, GL even needs a reboot in a more serious tone before the JLA could be done right. Film it in a realistic style and with deeper meaning then a large action movie. And when they come together at the end or they finally unite at watchtower for the first time, don't have them in costume. Have them as Bruce Wayne, Clark Kent, Hal Jordan, Diana, etc. Although superhuman, show their humanity. Normal people with normal lives, with abnormal abilities and responsibilities.
Maybe way off base and may make no sense to most, but like I said, I can visualize what I like in a story and film, just hard to convey.