What does it take for a new character to gain a foothold of popularity in today's comic book world. Every superpower imaginable has been undoubtedly done, so the only thing I see that can remain as an attraction is the character's background and personality, and at this point we've seen character's with every personality type, and from walk of life (and death) has been done. What would it take for a new character to find a place in your heart?
Keep in mind that any new guy who comes along will instantly be compared to a bigger name that came before him. If we create a new mercenary character they'll instantly be compared to the likes of Sabretooth, or Cobalt Man. If we try to create a genius character they'll get compared to Tony Stark, or Reed Richards. Fans love their old-time character's so much that the odds are instantly stacked against a newcomer.
I would say give that new character their own on going series so that way, fans would be able to see that new character being different from the other characters who have been around. Some fans love seeing different characters and as long as that new character has something different to offer, then fans will enjoy that character.
Original ideas I think. Even if they are ridiculous like, say, Axe Cop. A brand new idea gets the fans going. Or if you're going to use something that needs to be put to rest *cough* super powers *cough* you need to put a new spin on it. Like Kick-Ass or the Boys.
The other thing that I think is essential is depth. Taking The Walking Dead for instance. While it's dialogue is written horribly it is continuing because it's interesting. Not because it's about Zombies. But because it focuses on the collapse of the "stable" human being.