I'm most interested to see if Rondo can put his game together to the point where he's a double-digit scorer practically every night. Rondo scored in single digits in something like 36 out of 80 games last season. To become an elite point guard, he needs to be scoring 10+ almost every night.
Also, of course, I'm curious to see how KG recovers. It will be exciting to see Rasheed and Marquis, too, but I'm most interested in Rondo and KG; those two are the key to a championship for us, I think.