Sounds like a very smart move to me. Even our own Danny Ainge has admitted that there are only two (immediate) impact players in this draft: Irving and Williams. With this move, the Cavs take advantage of LeBron's departure and their #4 pick to secure the two best players in the draft. They don't really lose much because Williams is significantly better than anybody they'd get a #4 (Kanter), and they aren't going to get any really good players with that trade exception otherwise.
Moving forward, they'd have Irving, Williams, Varejao, and Hickson as a core group. That's not spectacular, but it's very solid if the two new guys can reach their potential.