Trades don't start coming out until I believe late next month, early June. I'd check out the trades to Snyder's Batman, Morrison's Action Comics, Azzarello's Wonder Woman, Johns Aquaman (it actually is a good book), some of the other titles that others have praised in the thread like Flash, Batwoman, etc.
Would I consider Justice League a "gateway book"? No not at all. Nothing in the origin arc really ties in to the other books since Justice League takes place five years in the past of the New 52.
Thanks for the suggestions Admiral.
In regards to JLA, I think it's lack of hard ties to the other books would make it the gateway book, especially with it being in a different time frame.
So a noob could come onto JLA, get all the big name heroes, and if they wanted a deeper exploration of those characters, go to the solo books. The characters themselves would also be more thought out in terms of how they act etc.
I generally remember that back in the old days, characters acted the same regardless of where they appeared. But in this newer, shorter attention span era, you have to maybe hook them with a slightly different approach in one book.
From what I understand, Hal is an arrogant ass in JLA, but not in GL. Do arrogant assholes work better to draw in noobs? Maybe.
How cohesive is the new universe presented? Is it fairly tight, or are they going for something looser so as not to have to worry about crazy continuity stuff? If so the latter, that might explain the character difference.