Excerpts from Keith Law ESPN Insider:
"His contract is quite favorable, $24 million guaranteed for the next two years with an option at $13 million ($1 million buyout) for 2018, which will almost certainly be picked up if he's healthy. But even if that comes to pass, the Red Sox will be lucky to get even 6 WAR of value out of Kimbrel over those three seasons. You have to place a huge premium on the closer role -- high leverage, but not always the highest leverage situations -- to believe he's going to be worth close to what Boston gave up.
Boy, did they ever pay a steep price for him: two prospects among the top 50 in the game and two other prospects of significant value. Center fielder Manuel Margot is the best prospect heading back to San Diego, and he's exactly the player the Padres needed to get back in a trade this winter. The Padres didn't have a true center fielder in the system, and Margot is a plus defender there who should be able to handle the large territory in Petco Park. He's a disciplined hitter who rarely strikes out and has the swing to hit for at least average power when he fills out physically, although his home park won't help him in the home run column. He has outstanding instincts on both sides of the ball, and I imagine it killed the longtime Sox employees who've watched him develop the past few years to see him go.
Shortstop Javier Guerra isn't far behind Margot, less polished right now but with enormous upside; he's a plus defender at shortstop with plus raw power and a good chance to hit for average, too. Guerra has soft hands and very easy actions at short, a natural at the position who should be a legitimate asset in the majors with his glove. He has great bat speed that generates a lot of power, and his contact rate kept improving as the season went on -- 29 percent in the first half, 19 percent in the second -- after I saw him having some timing issues in mid-June at Lakewood. He could truly be a monster of a player; a good defensive shortstop who even hits .280 with 20-25 homers is a possible MVP, although Guerra has yet to reach high-A and is probably two years out from the majors.
The Padres didn't have any need for a $12 million-a-year closer, although they'll probably pick someone up to handle the ninth inning. But they had several holes to fill in their system and just addressed several of them, getting a lot of upside in the deal but with two of the four players close to major league value. Margot alone could be more valuable than Kimbrel by 2017, and Asuaje should be a positive asset by then, too.
For Boston, even if you think it's fair value because you believe the ninth inning is some super-woo time that only the few and the proud can handle, the Red Sox just traded two of their most valuable minor league assets for a 60-inning reliever … which means they can't trade them for something else they need, like a high-end starter. It's not a great start for the new regime's first offseason."