Criticizing Obama does not mean you want him to lose, it means you want him to win. We criticize things in order to make them better. And that is the crux of the problem. If you believe Obama got everything that was humanly possible in all these deals then of course the people opposing him look like bitter whiners with nothing productive to offer. But there's another line of thinking that argues Obama could have gotten a lot more in all these negotiatons but didn't, and we have to do something about that. There have to be consequences. We have to make him demand more.
Those Obama supporters on the Left who insist your only two options is to vote for Obama without reservation or consider yourselves complicit in any Republican gains have got a lot of nerve trying to crown themselves the sole rulers of what constitutes acceptable Democratic behaivor. But they're right. Not voting for Obama does make you complicit. But those on the Left who blocked Obama from criticisms for two years and went Jihad on those who complained are complicit as well. So is Obama. If he wants to get re-elected then has to do the things necessary to get those votes. He has obligations as well.
I don't remember when the Left decided that criticizing our elected officials in public was a bad thing but I remember it sure was popular to Democrats when Bush was President. We tried the Clap Louder method for two years and it was a disaster (just like it when Bush was president--you'd think they'd had known better).
Update: Also, just because you're unhappy with Obama doesn't mean you aren't working in the background on other Democratic elections throughout the country. There is more to the Democratic party than Barack Obama. We would do well to remember that.