The Celtics are sixth in the league in point differential, and closer to third than to seventh. They have a better +- than the Bulls, Heat and Raptors, despite having a worse record than all of them. I don't necessarily think the C's are better than all of those teams (particularly the Raptors), but we should feel really good about how these guys are playing.
Also worth noting: right now there's the Warriors, the Spurs, and everyone else. I expect the Cavs to gain ground as they get healthy.
1 Golden State Warriors 15.40
2 San Antonio Spurs 10.40
3 Indiana Pacers 5.57
4 Cleveland Cavaliers 5.54
5 Oklahoma City Thunder 5.52
6 Boston Celtics 5.13
7 Toronto Raptors 3.85
8 Miami Heat 3.65
9 Charlotte Hornets 2.58
10 Orlando Magic 2.28
11 Atlanta Hawks 1.55
12 Utah Jazz 1.37
13 Chicago Bulls 1.15
14 Los Angeles Clippers 0.91
15 Phoenix Suns 0.51
(... 30 Philadelphia 76ers -10.85)