He is certainly not without fault- Strike in1994, steroid scandal, All-Star Game tie, and my personal favorite- trying to contract the Brewers biggest competitor the Twins. That was just wrong.
That said, he has brought labor peace- something unheard of in baseball, and really unheard of in most pro sports- including the NFL. He brought in the wild card, looked at expanding the playoffs, brought in interleague play, started the World Baseball Classic, and any problems that have arisen in baseball, he went ahead and took measures to correct them. There are new and or renovated stadiums in almost every MLB city as well and he brought MLB back to Washington DC and out of Montreal. Baseball has continued to grow its international roots- especially in Asia.
I think that there will be more things coming such as draft reform, and last year MLB had a committee with all kinds of baseball people- players, managers, owners, former players, writers, etc.- to discuss all kinds of issues such as what we are talking about right now.
Maybe I just remember how bad Fay Vincent was to appreciate what Selig has done. Vincent did not want to change anything with baseball- and he was killing the sport. He was an uber purist. And had Bart Giamatti not died, I think he would have been equally as bad. All he did is sit on his *** and write poetry about baseball and suspend Pete Rose.