Extinct human species: how different were they from us?

Well done Homo sapiens! Yes, that's us: the modern human. We avoided extinction and thrived. But this was not the case for any other archaic human species. And if you think that we simply evolved in a direct line, you couldn't be more wrong. In fact, other species of humans cohabited on our planet at the same time. And yes, we even bred with some of them. Though in the end, we were the only ones who made it to this day.
But how different were these early human species from us, really? 
Extinct human species: how different were they from us?