As for what the first episode contains, its a pretty logical stopping point.
You have to learn what makes Ellie special by the end of the first episode, and how they discover it is a bit better, and more tension-filled than the way they did it in the game.
At the same time, if there are people who do not know the video game, then they don't know that its just going to be Joel and Ellie here soon. So there's no point in having certain people die just yet.
Just about everything occuring in this episode is given a more-logical reason than in the video game.