Thousand Winds is a 5/6 flyer for costing 4UU (4 generic/2 Blue) to cast. Those are fair stats for a 6 mana creature. It also has a morph cost of 5UU (5 generic/2 Blue). Morph creatures allow you to play them face-down as a 2/2 creature for 3 generic mana. Then, you can pay the creature's Morph cost to flip it face-up. When it is flipped face-up, most Morph cards have an effect. With Thousand Winds, when it is flipped face-up, you return all other tapped creatures to their owners' hands.
At the time, it was clear that this flyer would be an interesting card that would play well in the Arcanis the Omnipotent deck included in the Speed vs Cunning Duel Decks. But, because of the large mana investment, it wouldn't see much play outside of Khans of Tarkir Limited environments such as drafts and sealed deck. It's also an underwhelming creature unless it's able to be flipped face-up. As good as the effect is, it's extremely situational.
However, Thousand Winds does see some play in EDH. Commanders that have utilized the Morph creature include Ixidor, Reality Sculptor and Kadena, Slinking Sorcerer, who are all about the Morph creatures. There's also Animar, Soul of Elements, who can cast it for much less with his effect. Unless you're building a Morph-themed deck, though, Thousand Winds is a flavorful but not very efficient creature.