Playground Games have invited some select people to play Horizon 3, and the curfew on the game footage they recorded lifts today, so there's plenty of new gameplay videos out on YouTube. I haven't gotten around to watch much of it yet, so feel free to add videos you recommend to this thread. My first recommendation is Failrace:

He shows off and discusses some of the customisation options, does an offroad race, and also talks about the openness of the map. Cool stuff!