I think Danny's draft day statement about him is accurate - he'll make a good 6th man.
I agree with what most people have already said on the positive parts of his skillset. He passes well, has a good BBIQ, runs the break well, and at least knows what he should be doing on defense, even if he is not always able to do it. He also has a nice touch around the basket when he gets room to operate, whether that's on a back-door move or on the break. I like him.
That said, I think those projecting him as a star need to pump the brakes. There was one post comparing him to Joakim Noah (I won't even touch the Dirk comparisons), but it falls short because Noah has about 5 times the motor AND (more importantly in my book) the boy (Noah) would rather die than lose. Those back to back NCAA championships showed me a lot about his attitude, even then.
And that is the one piece that, for any upside that can be found with this team (be it KO or anyone else - and there IS upside there) I don't think they have much chance of doing well now or in the future. There isn't anyone on this team that hates losing more than he loves winning. THAT is the piece that, even more than their talent, the Celtics lost when PP and KG were shipped off to Brooklyn. Until that level of killer instinct enters the locker room again, the Celtics will be lovable but mediocre. Olynyk doesn't have it, Sully doesn't have it, Green sure as shooting doesn't have it, and even Rondo, despite his spectacular ability to play with a gruesomely dislocated elbow, doesn't have it.
That said, I'll still root for the Celtics just as hard this year as I have for the past 25 years.