I think it's a pretty decent trade, asset-wise, from the Cavs' perspective... sure, four(!) picks is a lot to give up, but Deng is probably a top 5-7 SF, plays well on both ends, and will be a quality player for the next few years. I've seen worse trades.
This must signify that they're throwing in the towel on the whole "Bring LeBron back to Cleveland" thing. Not that it was ever anything more than a huge longshot anyway.