Great acting, terrible characters

You say terrible characters but you only talk about Lu, she would only make one terrible character. What made the other characters terrible?

I found them all to be believable (not so much their actions, but, as I already replied to you in another comment, if it was 100% realistic we wouldn't have a movie) and I could understand why they behaved the way they did. Maybe, to understand or like this movie you have to relate in some way to the characters. At least for me, I think being able to relate to them made the movie a good movie (I like portrayals of imperfect people that have a lot of stuff to figure out yet and I can relate to that).

I agree! Ellen Page plays a flat,smart Alex character just like in Juno. Can she even act?

Well, it was not her, the character had many redeeming qualities. So, there must be something missing in your heart, if you are unable to feel it. You could not stand her, which sounds like anger, so I would guess you must be seeing yourself in her, some aspect of yourself that you do not accept.