A whole host of characters in a setting disconnected from most of what DC usually trades in. Traditionally, the only connection is Superman, and DC isn't doing what they can to make him popular to a new generation so a tertiary brand associated with him isn't getting a big starpower boost.
A massive roster of characters that rivals the X-Men in some of the latter's incarnations, but all contained in only one book. Tons of interpersonal history and complicated origins. This is refreshing to some, a curse to others.
They're mostly all aliens. If SUPERMAN is too alien for some, hoo boy, the Legion is as far out as it gets. This is refreshing to some, a curse to others.
They're inherently a little silly. Matter Eater Lad. He either rules or you hate him, and a lot have similar premises. This is refreshing to some, a curse to others.
Nothing that happens in that book gets influenced or influences anything else. In an era where readers have been conditioned to follow the inertia of events, it's always left by the wayside. This is refreshing to some, a curse to others.
There are lots of reboots which provide hard beginnings and endings for each version. This is refreshing to some, a curse to others.
Seeing the pattern? It's not a traditional superhero comic as they've morphed into in ways that make it easily acceptable. Hell, it USED to be the last bastion of absence from Batman until we got Planet Gotham. Thanks, Bendis. :P