Well, Burton's right that from Pittsburgh's perspective, it's a horrible deal. Another offensive forward with a high cap hit who's pushing 30 was not what the Penguins needed to push them back over the top.
And the fact that they've got $6.8M in cap space tied up in Kessel in long term, and tied up most of the premium future assets they've got left in the Kessel trade (their 2014 first rounder, and their 2016/17 first and second rounders) means they don't have any of that available to them to address the team's needs. Imagine how much farther ahead they'd put that cap space and those assets towards fixing their blueline?
From the Leafs' perspective, the deal was still pretty underwhelming. It sucks that we retained salary, got a first round pick with a lot of conditions attached and that we also have to give them back a second round pick.
But the gamble Shanahan & co made was that if Kessel came back and still dogged it with Babcock behind the bench, or if he finally started running into injury problems, or if he dropped significantly below the 30 goals/80 points he'd been scoring for us, there would probably be no getting rid of him at all. With Kessel on pace for about 20 goals and 50 points, that's looking like a pretty solid bet right now.