I'm gaining confidence in Brad Stevens as a GM every time he makes a move. There's a logic and coherence behind each one. He's improved this team more since he took over than the last several years by the former regime (I still don't think Ainge was making those decisions).
He's shown creative use of the salary cap, the ability to get lottery ticket/high upside players on the edges of the roster, the ability to get solid role players for nothing or very little (Richardson, Horford, Kanter), the confidence to invest money in players he believes in (Smart, Richardson, and Williams) regardless of fans approval, and he has patience with young players (Langford, Nesmith, Pritchard, Williams) even though most fans want to trade them, and the ability to cut ties even if the team invested in a player (Parker, Fall).
I expect him to make a bigger move this trade deadline or off-season, but the maneuvering he has made has impressed me thus far.