I don't understand why Jacob was allowed to deceive Isaac to get the blessing that belonged to Esau, and why he was allowed to take that blessing. Furthermore, what was he doing dressing up as Esau, which certainly seems to indicate that he knew he was doing something wrong? If receiving the blessing was justified, why didn't he just explain that to Isaac and get the blessing with his consent?
Jacob's seeming "Esau complex" is one of the more complex topics in the Torah, so I empathize fully with your question. But allow me to present only some of many possible explanations:
First of all, while Esau had the potential to be a very righteous person, he wantonly chose a path of wickedness, and cunningly deceived Isaac into thinking he was the person that his father wanted him to be, and that he could have become if he wanted. But instead, according to traditional sources, he was a glutton, a murderer and an adulterer who "trapped his father with his mouth" by presenting himself as if he meticulously observed Isaac's ways.
This is why Isaac thought to bestow the blessing upon Esau. But Rebecca, exemplifying what the Sages describe as a woman's keen judgment of character, saw the truth about her wicked son Esau. She therefore understood how dangerous it would be to have such blessing in the "hands of Esau", and sought to secure the blessing for Jacob, who deserved it and would use it properly.
According to one explanation, this blessing was earmarked for the first-born, so that when Esau gluttonously despised the birthright and sold it to Jacob, the right to the blessing was transferred to Jacob. Jacob didn't tell Isaac of the sale because he did not want to make Esau look bad, nor did he want to hurt his father over Esau's despising of the birthright. But Esau knew that he forfeited the blessing and that it really belonged to Jacob, and yet he continued to deceive his father and went along with his plan to bless him. So it was not Jacob that was deceiving his father to get Esau's blessing, but rather Esau's deceiving him to get Jacob's.
So why didn't Rebecca or Jacob intervene by revealing this directly to Isaac; why did they contrive a deception of their own? Because at that point, time was of the essence, and if they had revealed the truth of Esau's ongoing deception of Isaac, he, convinced of Esau's sincerity, clearly would have consulted with him about their accusations. At that point, Esau would very likely have murdered Jacob, which he ultimately intended to do, and which was the reason Jacob fled to Rebecca's family. So Jacob was justified in protecting himself through cunning that which Esau intended to steal from him through cunning.
According to another explanation, the blessing was not necessarily earmarked for the first-born, but rather it was intended by Isaac to be for Esau. But this was because, even in Isaac's understanding of the two brothers, Esau was more interested in this-worldly matters while Jacob was focused more on spirituality. Accordingly, Isaac intended to give Esau the blessing for material bounty in order that he would help support Jacob's Torah study, which would in turn benefit Esau as well. He thought that the brothers would maintain this mutually-beneficial relationship, as did later the tribes of Issachar and Zebulun. Rebecca knew that that was the farthest thing from Esau's mind, but rather he would take the blessing for himself and not share any of it with Jacob, effectively strangling the life-line of Torah. She therefore had Jacob "dress-up" as Esau, meaning she equipped him to be involved in this-worldly pursuits, in order to receive material blessing for the purpose of supporting and studying Torah.