Personally, I think this whole number retiring thing has gotten out of hand. Sorry, but there should be a much higher level for a number to be retired. As much as I love KG, 4 years and 1 championship does not deserve a number to be retired.
The only on this list would be Pierce. Not only has he put in his years, but is 2nd or 3rd all time leading scorer in Celtics history. I can get on board with that. The other 3, not so much.