Journey is the only game I found worthwhile. The game still gives three interesting titles that are worth playing in the idea that they approach games as art. While unique, I would say play other full disc title first instead.
I'm glad I finished Journey prior to writing this because it is worth finishing. I've played all of thatgamecompany's released titles, but Journey was the first to disappoint me. It was just too slow. Even my daughter, who I thought might enjoy its simple controls, was too bored to play it.
But it does pick up and has enough "wow" moments to be worth recommending. Not as good as my expectations, however. I especially didn't like that the gameplay was a modified version of Flower and some moments of hiding from enemies. It's just such an overused and tired form of gameplay, avoiding a character's flashlight essentially, that it took away from the experience. I also didn't like you didn't interact much with your traveling companion.
Flower I also beat to the end, and it is probably my favorite of the collection. The music is great, the visuals great, the gameplay fun and fresh. Some parts are frustrating because moving with the controller is not terribly precise. And I like the pro-environment message.
I have not spent much time with Flow because although I like the idea and presentation, it bores me after a while.
The unreleased games are minor interests -- a shooting game where you face rounds of enemies, a tower defense game, and a cool game where you shoot enemies on a static screen and collect their skulls. I didn't see much reason to play it beyond 10 minutes, but those were a fun 10 minutes.