What is the significance of the Berachah that Yitzchak gave Yaakov here?
Ha'amek Davar: He endorsed his actions (to show that he did not hold what he had done against him).
Malbim: He blessed him with the world to come, and another Berachah below (verses 28: 3,4, to have many children, and receive Birkas Avraham and inherit Eretz Yisrael).
Why does it say that he called "El Yaakov" (and not "l'Yaakov)?
Ha'amek Davar: L'Yaakov implies that he is not there, and he calls him to come. El Yaakov implies that he is already there, but he calls him to endear him. Yitzchak needed to call for Yaakov - he was ashamed to come, for he tricked him - and then endeared him, to show approval of what he did.