It's been the same story all season:
1) Poor rebounding - in part because our bigs don't block out and in part because our team has a general lack of athleticism.
2) Lack of interior scoring. Our most reliable scorer within 5 feet is Perk, and he can't succeed on offense unless everybody else is hitting shots so he is left open. He can't score 1 on 1. KG is now primarily a mid-range jumpshooter and Rasheed...well, Rasheed is different things on different nights but in general he's not reliable from anywhere. Davis is too stumpy to finish around the rim in traffic consistently, especially when the defense pays attention to him. Shelden Williams is just not a good offensive player.
3) Inconsistent outside shooters. There are games (like the latest game against the Spurs) when all of our shooters go cold and we can't hit anything from beyond the arc. The C's almost always lose those games, especially against decent teams. Unlike Orlando, the Celtics don't have the best rebounder and put-back-er in the league to help them out when the outside shots aren't falling.
4) Lack of bench offense - nobody on the bench can create their own shot. Thought Nate would be an improvement but he hasn't been.
5) Inconsistent slashers. At times, Rondo takes over games with his ability to drive to the hoop. Occasionally, Paul Pierce does the same. Indeed, even Ray Allen gets in on that action sometimes. We've seen Marquis Daniels have some good games cutting to the rack, as well as TA. But we've also seen far too many games - important games against good opponents - where most or all of those players disappear in that regard. I don't think I've seen a game yet where Rondo is able to drive the lane for the whole game even when the opposing defense starts trying to clamp down; in fact, as soon as the defense game-plans for Rondo, he seems to stop scoring. Paul Pierce used to be our main option for driving the lane, and he could do it very well, but this year with the decline in his speed, athleticism, and overall game he's become more and more an outside player and those cuts to the rack have become rarer.
6) No superstar. When things get tough, when the opposing defense really clamps down, when the offensive sets aren't working, the Celtics really need somebody who can just step up and take over the game - somebody who can will the team to victory. The Miami Heat are not a very good team but they're still managing 40 wins and are heating up late in the season because they have a player who wins them games on his own. The Lakers have won quite a few close games this season because Kobe takes over late in the fourth when the rest of the team fades. LeBron is a one man team. When everything goes right, it is possible for a team of great players without a superstar to play very good team basketball and win when it matters. It happened for Detroit in '04, and we saw it happen for us in Boston in '08. I just don't believe the '10 Celtics are that kind of team. Indeed, there really isn't a team in the league like that this year, in my opinion. In June, a superstar will hoist the trophy.
The bottom line is when the outside shots don't fall, this team has a really hard time scoring in the paint; it's that inability to score inside or make up for the low fg% with aggressive rebounding that will ultimately spell their defeat in the playoffs. Right now the Celtics are a better, more experienced version of teams like Portland, Chicago, OKC, Charlotte etc who all play very well for stretches but fail to play great consistently because of their lack of an inside presence. There's a reason LA, Cleveland, and Orlando are the 3 best teams in the league - they have superstars, and they have great interior guys.
Note:
I posted this in response to the "C's flaws aren't going to just disappear thread," but I decided to make a post of it since I spent a while writing it and didn't want it to get lost in the shuffle of things.
I'm not happy to say any of this, but I think this is a complete assessment of the Celtic's issues this year, and I don't see how any of these issues are going to magically go away next month. Even during this latest stretch, we've seen some good things but not enough, and not against the harder opponents. Nothing we've seen recently or at the start of this year changes any of the 6 problems I've outlined.