The litmus test that's been established: if there was a big-budget movie about the character, what would you put in Thirty-Second Movie Trailer?
Ten years ago, when most superhero movies were well-known for Entirely Missing The Point Of The Character, that would have been a terrible test. More recently, however, producers for screens large and small have managed to pull off exactly that: X-Men, Spider-Man, Batman Begins. honestly, the trailer for Daredevil managed to capture more of the character's "woo" than the movie itself did.
Recently, a two-minute trailer for Mercy Reef, an Aquaman series by the producers of Smallville, appeared on YouTube -- but got yanked by Warner Bros. The series, alas, is not on the fall schedule for "The CB", the bastard offspring of UPN and WB; based on the quality of the trailer, fans and former sceptics alike are now hoping to see it as a mid-season replacement. It certainly captured the frisson of woo for the character, in a way that the comics haven't managed since the '60s.
A better example -- and one that we can actually see, for a film that actually will hit the screens -- is Nicholas Cage's Ghost Rider.
In a word...