I had a similar reaction when I heard about it. Not as strong as yours, I'm sure, as I'm neither gay nor American, but basically I read about it, saw a short clip video and thought "so, what does it change?"
Even the very short clip was obviously Obama saying "I personally think people should be able to marry someone of the same sex... but I'm not going to do anything about it. You know, it's just my personal opinion".

When people started praising him, I tried to understand what the big deal was. People said it's the first time a US President has stated his support for marriage equality. Maybe the symbolism is important to them because now, people might be able to state publicly that they're in favour of it, rather than have to hide it to have a chance to be elected.
If that's the case, I find it pretty sad. The personal opinion of political figures should not matter. I wish the President was able to make a statement to that effect. Even if he was against it. I would have preferred if he had said "I'm not comfortable with homosexuality. But what I think doesn't matter. What individuals think doesn't matter, no matter how prominent they are. What matters is that human beings should be treated equally. So I'm going to pass marriage equality into the law, because what matters isn't my personal feelings, it's not my comfort level, what matters is that I'm the President of all Americans, regardless of religion, sex, race or sexual orientation, and I owe it to them to give them all the same rights."

It might sound ridiculous that someone who isn't comfortable with homosexuality would put his personal feelings aside and make same-sex marriage legal, just because it's right and fair. But Obama basically did the opposite. He stated his personal feelings, and then put them aside, in favour of injustice.

Now, he's running for President while openly for gay rights, and I hope he gets elected. But I'm not convinced it will make a huge difference if he still insists on doing nothing about it. Maybe some people will feel like they have an ally at the White House, but will it really helps? If you're being bullied, does it actually help to have a friend sit idly if you know that in their heart, they're on your side? I'm not convinced. Maybe you'll feel a little bit less lonely knowing that you have some silent support, but they're still a lousy friend.