Proposition 8 fails to advance any rational basis in singling out gay men and lesbians for denial of a marriage license. Indeed, the evidence shows Proposition 8 does nothing more than enshrine in the California Constitution the notion that opposite-sex couples are superior to same-sex couples. Because California has no interest in discriminating against gay men and lesbians, and because Proposition 8 prevents California from fulfilling its constitutional obligation to provide marriages on an equal basis,the court concludes that Proposition 8 is unconstitutional.
That's the conclusion of the 135 page ruling on the case by Judge Vaughn R. Walker, which you can read in its entirety here, if you're into that sort of thing.
This will get appealed, of course, perhaps all the way to the U.S. Supreme Court. Who knows what the Roberts court will do, given all the conservative Catholics there. But for now, we can all celebrate the fact that marriage equality got an important victory today!