The key passage in the ruling.
Denying committed same-sex couples the financial and social benefits and privileges given to their married heterosexual counterparts bears no substantial relationship to a legitimate governmental purpose. The Court holds that under the equal protection guarantee of Article I, Paragraph 1 of the New Jersey Constitution, committed same-sex couples must be afforded on equal terms the same rights and benefits enjoyed by opposite-sex couples under the civil marriage statutes.
You will hear screams about activists judges but you just go read that passage again. The ruling is based on the wording of a constitution written by the people of New Jersey through the legislative process. The judges simply ruled on the law. That's exactly the way things are supposed to work.
Source: Star-Ledger is probably going to be the place to be on this one.