Here is a summation of his blog post but you could (and should) read it in its entirety here.
1. Hesitating to take definitive action. McClellan was constantly preparing. According to him, the Army was never quite ready. The troops just needed a little more training. In his procrastination, he refused to engage the enemy, even when he clearly had the advantage. He could just not bring himself to launch an attack. When Lincoln finally relieved him of his duties, he famously said, “If General McClellan does not want to use the army, I would like to borrow it for a time.”
2. Complaining about a lack of resources. He constantly complained about the lack of available resources. He didn’t have enough men. His men weren’t paid enough. They didn’t have enough heavy artillery. And on and on he went. The truth is that, as a leader, you never have enough resources. You could always use more of one thing or another. But the successful leaders figure out how to get the job done with the resources they have.
3. Refusing to take responsibility. McClellan blamed everyone else for his mistakes and for his refusal to act. He even blamed the President. Every time he suffered a defeat or a setback, someone or something was to blame. He was a master finger-pointer. Great leaders don’t do this. They are accountable for the results and accept full responsibility for the outcomes.
4. Abusing the privileges of leadership. While his troops were struggling in almost unbearable conditions, McClellan lived in near-royal splendor. He spent almost every evening entertaining guests with elaborate dinners and parties. He insisted on the best clothes and accommodations. His lifestyle stood in distinct contrast to General Ulysses S. Grant, his eventual successor, who often traveled with only a toothbrush.
5. Engaging in acts of insubordination. McClellan openly and continually criticized the President, his boss. He was passive-aggressive. Even when Lincoln gave him a direct order, he found a way to avoid obeying it. In his arrogance, he always knew better than the President and had a ready excuse to rationalize his lack of follow-through.
