Some of these have already been said but here goes:
1. He is a male feminist. He highlighted the "women make 70 cents (or thereabouts) to a mans dollar" wage gap false "statistic" in the State of the Union address a few years ago. As someone else noted as well, his administration has aggressively pressured colleges and the military to go on witch hunts to satisfy a non-existent sexual assault/rape epidemic. This bothers me deeply; he is a traitor to his own gender.
2. Obamacare addressed a few of the shortcomings of the US healthcare system but really is a clusterfuck of epic proportions for many different reasons. It improved access to a small degree but did absolutely nothing to address current and future cost issues.
Even when they were working on the details before it was a law, the administration knew they were ignoring fundamental issues with the system but nonetheless, acted like they fixed everything when it became law. Obama and the democrats gave themselves WAY more credit than they deserved and were too egotistic to address major issues with the reform after the fact.
3. Royally fucked up with Syria with his "Red Line" statement. There is a PBS Frontline documentary called Obama at War that covers this in great detail.
The gist is: Obama told the Syrians he had their back if chemical weapons attacks occurred. They did and the Syrians were standing by for help; eager for US intervention that was promised if the "Red Line" was crossed. Obama, being the limp dick that he is, didn't do shit and ISIS came into Syria and took advantage of the situation and all the bitterness caused by Obama's screw up.
This is an excerpt detailing the aforementioned point (you can also see the full doc too if interested at the same site):
http://www.pbs.org/wgbh/pages/frontline/...-in-syria/
4. Taking sides and commenting on controversial criminal race cases that were still being investigated and/or in active trials. Very poor form from someone who is suppose to represent ALL Americans.
The biggest issue with Obama above all is that while he is intelligent, can give powerful prepared speeches, and has a seemingly calm and level-headed demeanor (for better or worse), he isn't a leader.
When he is in campaign mode, he is a master at PRETENDING to be a leader. But its just an act. And when the rubber meets the road and real leadership is called upon, he drops the ball more often than not. Hence, the massive sense of disappointment a lot of people associate with him now. There is no denying anymore, even among liberal people, that Obama at his core isn't a leader. There is too much clear evidence now that proves this.