He doesn't go down and talk to Pharaoh, but does this through his Godly ways. It isn't exactly clear how he does this, but he doesn't seem to be having a chat, it seems to be a much more supernatural thing. Pharaoh would have actually caved after just a few plagues, but God keeps him stiff.
The motivation behind this seems to be that Pharaoh would have in all reality changed his mind once the Israelites left. Maybe not immediately, but eventually he would decide to go get them back. So he forces Pharaoh to learn in the hardest way possible, so that it sticks.
He even does it right at the end. He allows Pharaoh to give the go ahead and dismiss the Israelites, then goes on to change Pharaoh's mind and give chase through the sea of reeds. But then he protects the Jewish people and closes the sea on the Egyptians.
Side note here: In movies and things the bit where they walk through the sea of reeds is a mad dash. In the Bible this event takes at least a few days.
...
Then the Jewish people have to get to the land of milk and honey. This takes a very long time. I'm not sure how old Moses is when they leave Egypt, but it takes right up to his death at 120 years old. And during that time these people repeatedly screw it up.
The most well known bit seems to be that when Moses goes up to receive the commandments from God, they make a golden calf to worship. They thank the golden calf for getting them out of Egypt, even. But then God shows up and they come back to him.
Then of course there's the deal where they aren't themselves permitted to enter the land, but only their children may, and so they have to wander the desert for 40 years.
Then of course there's the deal where they aren't themselves permitted to enter the land, but only their children may, and so they have to wander the desert for 40 years.
This actually happens repeatedly in various ways. They won't go to war because of the enemy's superior numbers, so God punishes them. And when they try to go to war without his go-ahead they are punished, too.
At one point some of the Israelites who are not descendants of Levi decide that they want to be priests, and they follow all of the directions, but God doesn't like it and sends a plague that kills 14,700 people (I think that's the number).
I can't think of the other times this happened, but I'm pretty sure there are a couple more.
God calls the descendants of Jacob a "stubborn people," but I have to wonder. Maybe he did the same thing to them. Maybe he decided that the lesson to stay loyal to him, that he would protect them, wouldn't really stick unless he put them through quite an ordeal. It's not said explicitly. It's not even suggested, really. They just seem... honestly kind of dense to not catch on to how things work.
But that's my hypothesis about the Pentateuch. I'll let you know when more cool stories come up.