Jason Terry is actually playing better than he did last season in Dallas. People are letting their eyes lie to them.
Look at his numbers. Turnovers way down, and although scoring numbers are slightly down his efficiency is better (his TS% last season was 54 ... this season it is almost 64!!).
Terry is not the problem. You could argue that Doc needs to give him more minutes, but Terry is playing well.
Sullinger is also playing well. His defense isn't great, but he isn't the sieve that some people here seem to think he is (in fact, he is actually blocking shots at a decent clip for the amount of minutes he is playing ... his only big problem is over fouling). Still, his rebound percentage is exactly what you want out of a rookie big man, and his shooting percentages are above average. I actually want him to get more playing time, in all honesty.
Wilcox, too, has been great for us. His rebounding has been sub-par, even for him, unfortunately, but his scoring has been much appreciated. His alley-oop receptions skew the data a bit, obviously, but his TS is an astounding 78%, and his PPS is an even 2.0. He also has solid defense, and draws fouls at a good rate.
Pierce is also playing well, despite his shooting slump. He has actually been playing pretty good defense (in fact, the stats say better than last season). His rebounding has been great, as well. He just needs to get his shot more consistent.
Courtney Lee has been a big let-down so far, sure, at least on offense. His defense has been solid, though.
Bass has been sub-par, as well, though only insofar that he has been inconsistent. He has had a few beastly games that show what he can do. But he has definitely been up and down so far.
Honestly, KG has been a disappointment too. I hate to say this, because he is my favorite all-time player, but he has been really off. His defense is virtually non-existent (okay, that's an exaggeration, he still plays pretty good defense compared to the league average, but it isn't nearly as good as you should expect from him). He has been good on offense, but his passing and rebounding are both down.
Jeff Green has, unfortunately, been our worst player. I hope to see him improve, and expect he will, but he has been downright terrible so far.
My expectation is that KG and Pierce will improve as the season goes on. Both are still producing [dang]ed well for players their age, and just need to get their defense and shooting, respectively, back to form. We can pretty much assume they will, as those have traditionally been their greatest strengths. Bass and Lee, too, are have historically played a lot better, even on relatively limited minutes, so they should improve a bit as their roles and minutes become more consistent. Jeff Green is the X factor, and whether Barbosa will be able to keep up his hot shooting.