The Celtics are a very talented but young team that at times, displays some growing pains. This is true of individual players and Coach Stevens. I think back on how many wanted to give up on Marcus Smart for example, a flawed but impactful player. Stevens is like that, yes young and not fully seasoned (think how many years Spoelstra has been coaching), yes, not perfect, but I am for hanging in with him as the coach.
I think he is a good coach by NBA standards, not coach of the year but solid. I think he is a good match for this young team, and a good match for Danny Ainge. In some more years (Spoelstra has 12 years as the head coach and 25 years with the heat organization, Stevens has 5 years in the NBA) we are going to look back and realize he has been good for a long time. It will kind of sneak up on you like Spoelstra has kind of snuck up on the league. That is my prediction anyway.