There's a problem with ongoing superhero comics from a storytelling perspective, they never really end. It's different with novels and limited series, those have a beginning and an end, then the story is over. Not with ongoing comics, and I find this problematic. The problem is great stories from great writer's usually sell really well and thus the companies that publish them, usually owning all rights to the characters, want to make more. I am not dismissing the quality of Before Watchmen but The Watchmen didn't need anymore than what it already was. It has a beginning and an end and everything in between is really fantastic.
Spoiler alert for issue #20 of Green Lantern. At the end of that Geoff John's caps off with a glimpse into the future of all the Earthborn Green Lantern but the problem is there is still going to be an issue #21 and that writer is going to want to put his own spin on the mythos, changing what has been established and essentially either relegate that story to meaninglessness or tarnish it with half concocted plots. I am not insult Robert Venditti who is taking over Green Lantern but making an implication of all future writers of an ongoing series that takeover for another writer.
Transmetropolitan by Warren Ellis is another series that ran for a good 60 issues but it had a proper ending that Warren Ellis wanted to tell and then it ended. The same goes for Neil Gaiman's run on The Sandman for 75 issues. I'm sure with his new Sandman series he has written he has a set limit of issues he needs to tell his story because he knows stories need an end.
The problem is with writers on runs of company icons like Superman, Wonder Woman, Batman, Spider-Man and etc. that no matter how good of a run you have on that series, someone else is eventually going to take over and undo basically everything you've done.
Great characters can be ruining in comic books with oversaturation when they gain popularity. Wolverine had some of best comics in the past but now is in every Marvel book from the Avengers, to the X-Men to his own solo series. For the longest time Green Lantern had only one ongoing, then two, then three, now there are five ongoing comics related to the Green Lantern universe. All because a good writer wrote a good story and that sold a good amount of comics.
It's never enough with superhero comics to say that's the end and be done with it. It's part of the reason death in comic books has become so meaningless. Killing off a character sells comics, bringing them back from the dead sells comics and new characters are hardly given the chance because we won't let the old character's stories be over with. Sometimes it's okay to say "The end" and move on and as along as comic books keep ongoing the stories of the past will become less and less meaningful.