Bleed Cubbie Blue posts a very good interview with Len Kasper, the play-by-play announcer for the Cubs. I like his take on criticizing the team:

BCB: Do you and Bob feel at all pressured (either real or perceived) to toe the company line rather than express any true criticism of the way the Cubs are playing or of questionable moves that Lou makes during the course of a game?

LEN: No, we just do the games to the best of our ability. I think the holding back part is simply having a sense of decorum and understanding that 1) it's a very difficult game to play and 2) we're broadcasting baseball, not doing an over-opinionated talk show. We don't shy away from pointing out what's going on. I do it mostly by saying, "The Cubs are 0-for-their-last-20 in these situations" or "The Cubs have lost 9 in a row" or whatever. I treat the audience as thinking human beings who can form their own opinions. Yes, I have opinions, and they come out at times, but if I simply spouted them for 3 hours, I guarantee you, it wouldn't be a very enjoyable broadcast. Bob has his opinions too and I enjoy bringing those out, and he's not afraid to be critical at all. It's just that we don't normally scream those opinions. I think we do a thinking-person's broadcast and I'm proud of that. The biggest key for me is that we don't miss stuff. That's a huge goal of mine. I don't ever want to ignore something just because it goes against the Cubs or might not be a positive. We owe that to the viewers.

Len also knows VORP and OPS+.