I would be willing to place him in the top 5 defensemen of all time.  I say top 5 because I only go back to the 70's, so everything before that is only second hand knowledge.  Robinson is one of two players to have a plus/minus of 100 or more for a season.  The other player is Orr.  That's pretty good company to be in.

But, would I retire his number?  I don't think so.  There's something about the names of the guys that had their numbers retired, that when you hear their names, there's an almost reverance.  When people think of the Habs, they think of Beliveau or Richard, not so much Robinson.  On any other team, definately, but not on the Canadiens.