The opinion can be found here:
Here is my summary of the Court's holding:
(1) The Court held that it violates the California constitution to allow opposite-sex but not same-sex couples to marry, applying strict scrutiny for three different reasons:
(a) A fundamental right is involved (right to marry) under the due process and privacy clauses of the California constitution
(b) Sexual orientation discrimination is involved. Court holds that such discrimination is, like race and gender discrimination, subject to strict scrutiny under California's equal protection clause. Court further holds that you don't need to show current political powerlessness, nor do you need to show immutability.
(c) Fundamental right prong of California's equal protection clause
(2) The court held that it is unconstitutional to have a parallel scheme of"domestic partnerships." It leaves open the possibility that the legislature could change the name of "marriage" for everyone so that everyone gets a domestic partnership."