You know, funny enough, this series actually leaves me feeling strangely encouraged.
Lets look at the games in this series
Game 1:
Boston were without Brown - Celtics lost by 11 but it was much closer then that suggests. Boston led for most of the game and were right in it up until maybe the last 4 or 5 minutes. This was a winnable game.
Game 2:
Boston were without Brown and also lost Tatum for half the game. In truth though they were garbage in this game - lost by 22 points and it was well deserved.
Game 3:
Boston were without Brown and R.Williams, Kemba played terrible, and they won by 6 - largely thanks to Tatum's 50, but Smart and Tristan Thompson also stepped up in a huge way.
Game 4:
Boston were without Brown, Kemba and R.Williams, Brooklyn's big 3 combined for 104 points, and Boston "only" lost by 15 points. This really should have been a 30 point blowout considering the Celtics were basically missing 3 of their top 5 players.
Game 5:
Boston were without Brown, Kemba and R.Williams, Brooklyn's big 3 combined for 83 points, and Boston "only" lost by 14 points. Again, this probably should have been a 25+ point blowout.
It might seem like an evaluation, but really think that if Boston had Brown, Tatum, Kemba and Williams healthy for this entire series then games 1, 3, 4 and 5 all would have been very winnable. Even game 4, when the Nets played probably about as well they possibly could.
I know it's unrealistic to speculate about hypothetical, but I still find that kind of encouraging that if the Celtics top 4 guys were healthy through this series, it probably could just as easily be 4-1 to Boston right now.