Why do so many people dislike Obama?

I don't get why so many ppl dint like our pres. What dud he do besides make history in becoming the first black president of the us. Im not saying I worship him or like him or anything I'm just confused. He's our president so we should respect it . Also I heard if John mccaine were to be elected he would bring slavery back but then tht would go against the 13th amendment so...