My problem is that I'm always looking for a masterpiece for that style. I made an ESB that was technically perfectly according to style. I love it. Every commercial ESB I've tried (granted they are just the very commercial ones imported here), I would never buy another one.
There are many beers that I've tasted that were good, but they weren't outstanding, so I find myself not going back to them.
Or as another example, I'm always trying to find a way to like a certain style. I don't like saisons, yet I always try every saison my wife buys (she loves them), because I'm waiting for the one to convince me to like it. Same with IPAs. I've found one commercial IPA that I've liked, and even that one is just an average good beer for me. Oddly enough it's made by the most commercial brewery in this nation, Hansa. Every other IPA I've tried I've been disappointed with.
Then of course, there's the public's favorite type of competitions. Recently was at the "championship" version of that here in Norway (the winner got to brew with one of the bigger breweries here, Haandbryggeriet), and we were each given 3 plastic chips to drop in the buckets of the beers we liked. I happened to find two on the floor, so I got 5 votes. I tried every single beer in that place (over 100 beers, yeah a lot of people were drunk, and there was also a ton of beer poured out into buckets), and ended up going home with three chips still in my pocket. One I voted for because it was an Eisbock, and I've really been interested in attempting that style, but I honestly have no idea how it compares to others. The other vote was a guy who brought a Belgian trappist style that he had stored away for the last 6 years (he ended up winning). I only voted for him because if I had been storing a beer for that long, there's no way I'm bringing it to such a subjective competition. Oddly enough he won, and I truly believe it's only because of it being advertised so heavily as a 6-year old beer, and his guys who were helping at the stand were incredible salesmen. He himself was pretty shy and didn't talk with everyone that came by. Otherwise, it was even a really good version of the style. My wife loves Chimay, and even she stated how average his beer was. Other than those two, I found flaws in every single beer, or they were styles that I don't like, or both.
Point being, there's so many factors into what good is, as others have said, I don't think one could really ever come to a conclusion about it. It's too highly subjective.