I might be repeating somethings already said, but here goes--
Was God partisan in his dealing with the Israelites?
No, He chose them when they were nothing, had nothing to offer. He made the promise to Abraham to make him a great nation and give him the land of Canaan, but the greater promise was that the Savior of the world would come through his line ("all nations will be blessed through you"). An undeserved act of favor intertwined the line of the Savior with the nation of Israel. Therefore anything that threated to destroy the nation, threatened God's plan to rescue and forgiven sinners. (Also, God was not blind. He knew his nation was a sinful one. He taught, warned and even disciplined them so that they wouldn't destroy themselves and the promise they carried.)
Okay: What about Pharaoh? Did God treat him with justice, vengefulness or mercy?
Well, first remember that God gave him so many chances. "Let my people go!" "No!" <plague> "Okay, Okay! Go!" <pause> "Wait, you can't go!" Read the account. Each time it says "Pharaoh hardened his heart" Pharaoh, in spite of seeing the very real power of God, despite knowing with whom he was dealing, repeatedly refused to change. Finally, the change happens, "God hardened Pharaoh's heart" God no longer gave Pharaoh a choice. Just? Yes. Patient? Yes.
Remember why all this happened--The entire world was made of sinners, people who didn't love God or do what was pleasing to him. They all deserved (as we all still do) to perish on earth and suffer in hell. BUT, God is merciful and choose to send his Son. His Son would live a life of obedience in our place and suffer the torment of hell in our place so that we might have a right relationship with God. Pharaoh was standing in the way. Pharaoh was threatening the souls of millions, billions. God's actions were merciful, because they insured the salvation which the world needed (needs).