If anyone should get a different grade for the regular season and the playoffs, it's Chris Kelly.
Kelly was acquired from Ottawa in February with the goal of stabilizing the third line defense, aiding the penalty kill and winning faceoffs. For the most part, he accomplished these goals; Boston's penalty kill was at 80% when he arrived, and was 87.7% for the remainder of the regular season, and was 84.4% in the playoffs, with Kelly one of the primary PK forwards.
However, Kelly provided absolutely no offense in the regular season. With just 5 points in 23 games, it barely mattered how good his defense was; even on a third line, it wasn't enough to make up for his lack of offensive production. Kelly had the indignity of finishing the regular season with a -1 as a Bruin; not easy to do when you play for a team with the second best goal differential in the NHL. His GVT on the year was a 4.7, not bad for a third liner, but not anything to write home about, either.
Happily, the playoffs were a different story for Kelly. Kelly and Michael Ryder absolutely carried the Bruins to the crucial, series-turning game 4 win against Montreal, as Kelly had a goal and 2 assists, including some tremendous work setting up Ryder's overtime winner. (Amazingly, Kelly was denied a spot on the three stars.) And of course, the pivotal goal in game 7 that gave the Bruins a short-lived lead, and ultimately set the stage for Nathan Horton's heroics.
Kelly wasn't quite as good at faceoffs as advertised (47.5% in the playoffs), and ultimately, Rich Peverley (53.5%) ended up taking many of the draws that Kelly would have taken. Still, that was a modest price to pay for his newfound offense; he finished the playoffs with 13 points in 25 games, a +11 rating, and more than did his part to help the team capture Lord Stanley's Beer Mug.