Keeping it close: The Senators' success this season was all about the system, all about slowing down the game and slowing down the opposition. They weren't exactly a team that won by blowing out opponents, but rather by adhering to their defensive-minded approach. The question in the playoffs will be whether that system works for them in a best-of-7 series like it did in the regular season. It appeared that the Bruins figured out a key to playing the Senators in their final regular-season matchup, even though Boston lost 2-1 in a shootout, so that will be key to watch as well.
Enough defense: The question all season was whether the Bruins defense would be good enough. Now, after defensemen Torey Krug and Brandon Carlo each was injured in the final two games of the regular season, the question is whether they'll be healthy enough. There's no way to win the Stanley Cup, or even a round, without a good defense, and integrating inexperienced defensemen or moving players from the press box into the rotation is far from optimal at this time of year.
Coach vs. coach: The coaching matchup is an interesting sidenote to this series. Neither coach was in the NHL at this point last season, and yet each has led his team to the postseason. Boucher, who is in his fourth season as an NHL coach, is 11-7 in his career in the Stanley Cup Playoffs, having guided the Tampa Bay Lightning to the Eastern Conference Final in 2011. He has not been back since. For Cassidy, it's been even longer. The Bruins coach was 2-4 with the Washington Capitals in the 2003 playoffs, when his charges bowed out in the first round to the Lightning. That's not a lot of playoff experience on either side.