I jumped in for the early access since I had Playstation Plus. I didn't get to play as much as I would have liked in the extra week I had, but I thankfully had the chance to put some good time in this weekend when I needed a break from Mass Effect 3.
Hearing about the game, I didn't know what to expect. The notion of only having one other player in multiplayer, having it be a stranger, and not being able to talk to them at all seemed kind of weird. But it works. Very well.
The best analogy I can make comes from personal experience, jamming with friends. I play the guitar, some of my friends do too, and two others play bass and drums. When we sit, and chill, and just start playing, there's very little actual chatting. We don't say 'I'm going to play in this time, or 'I'm gonna switch it up'. We just go... we do our thing, and then everybody follows suit.
We riff on each other. Hear what the other person is doing, and decide how to react and compliment them. It feels remarkably similar in Journey. If I see another player walking in certain direction, or trying to jump to a specific part of the environment, or whatever, then I try to follow suit, or help, or get their attention and pull them in the direction I want to go.