Although some groups who are anti gay marriage are treating this as a win, the better view of the ruling is that it actually helps the case for marriage equality.
The High Court have ruled that under the Constitution, '"marriage" is a term which includes a marriage between persons of the same sex.' You can see the full judgment here. This now clears the way for the Commonwealth to make legislation allowing for same sex marriage, without requiring a referendum or reconsideration of the Constitution.
So although it is a very disappointing result for same sex couples in the short term, particularly those who were married and now have had the marriage declared invalid, in the long term, having same sex marriage legislated at a federal level is a far preferable outcome.
Having Commonwealth Legislation rather than state or territory laws means that marriage really will be equal, rather than having one set of laws for heterosexual couples and another for same sex couples.

There would have been different definitions of "marriage" and separate laws and systems for divorce. As a family lawyer, I was concerned that the ACT system would have created unnecessary cost for separating couples, confusion regarding the applicable law and may have resulted in substantial (and costly) litigation. It may have also created problems in the event of the death of either partner and what would happen to that person's estate, will and superannuation.
The Greens have now proposed the Marriage Equality Amendment Bill into the Senate, which provides for amendment to the commonwealth Marriage Act to remove discrimination on the basis of sexuality and gender identity.
Amending the Marriage Act really is the best way forward for true marriage equality and for equal treatment under the Family Law Act.
If you are a same sex couple and want advice about your current circumstances, contact Farrar Gesini Dunn Family & Collaborative Law for advice.