For the Bruins to be great, David Krejci must be great, too. Krejci long has been the key for this team — and, thus, at times, its most frustrating player. When he is really going, as he was during Rounds 2-4 of the playoffs last year, the B's are a matchup nightmare for any opponent. When he's not — which has been entirely too frequently — they are not of championship timber.