I'll start by saying that I hate Rob Blake, and that he shouldn't be allowed to clean-up the mess that he made with these contracts, but a lot of people here have absolutely no idea how to value Kings players.
Firstly, if you fail to understand that Sean Walker is nothing more than a cap dump, you seriously don't watch the Kings. I didn't even want Walker taking 3rd pair minutes last season, and said repeatedly throughout the season that I'd have dumped him for a 7th if possible. He's a warm body 6th/7th defeseman making way too much money, period.
Grans is still a very young defenseman, and with those you never know who/what they might blossom into, but he's stagnated in the AHL and just had a poor season. His time was running out with the Kings as he was nowhere close to making the Kings roster (he alternated between 2nd and 3rd pairing of unimpressive play in Ontario). He's been passed by Spence at RD in Ontario, Clarke is turning pro, and Doughty and Roy aren't going anywhere. He needs a fresh start, and I hope this works for him, but he didn't have 2nd round value anymore.
In this trade the Kings traded a massively overpaid AHL goaltender, dumped a overpaid 6/7th defenseman, a 2nd round pick, and a stagnated prospect at a position of strength to open cap space. This is a good job by Blake to try and dig a bit out of the hole HE created, but he should still be fired