If you take out the emotional attachment to Lester for a minute (a hard thing to do, considering.) The Red Sox made out really good on this deal, Yeonis Cespedes has established himself as a major league outfielder and hitter, and he still hasn't completely grown as a complete ball player yet. Its only his third year, he fits perfectly for this ball club because we desperately need outfield power. I think his average will start rounding out in the .280 range, and he's proven he can hit 30 HR's and drive in 80-100 runs. The lineup just got loads better with just one addition. Pedroia, Ortiz, Cespedes, Napoli is a hard stretch of hitters for pitchers to get through.
Back to Lester, I think its pretty telling that the Red Sox traded him to a team that has no interest in resigning him this offseason. I think it tells you they plan on making a serious offer to retain him for next year and beyond.