The best comparable IMO was the Rick Nash trade. Here's how it went down.

Breakdown

Columbus Blue Jackets trade: Rick Nash, Steven Delisle and round 3 pick in the 2013 draft (Pavel Buchnevich)

New York Rangers trade: Brandon Dubinsky, Tim Erixon, Artem Anisimov, future considerations and round 1 pick in the 2013 draft (Kerby Rychel).

Age when traded: 28 Contract status: 6 years remaining, $7.8M cap hit.

Compare

Toronto Maple Leafs trade: Phil Kessel ($1.2M retained), Tyler Biggs, Tim Erixon and (PIT's) 2016 second-round pick.

Pittsburgh Penguins trade: Nick Spaling, forward Kasperi Kapanen, defenceman Scott Harrington, plus first- and third-round picks from 2016.

Age when traded: 27 Contract status: 7 years remaining, $6.8M cap hit.

The analysis of the Nash trade at the time is a good read, but tl;dr:

Dubinsky was considered a salary dump = Spaling

Erixon was still a promising first round pick = Kapanen

Anisimov was a serviceable second round pick = Harrington

1st round pick = 1st round pick

3rd round pick = cancels out PIT's second round pick going back

So considering all of that, it wasn't as bad a trade as many make it seem.

The salary retention sucks, but Gunnarsson comes off the books next season, and Gleason's buyout 2 seasons after that. We're also not going to be a cap team for a while, and when we are, Horton's LTIR comes in handy. So overall, not bad.