I've been to a fair amount of improv at the Original UCB Theatre. When its the weekend shows and its one of the older groups, it's definitely better.
I had a friend taking classes there and I went with her to the Tuesday Harold Night where they have newer groups do a half-hour and you see maybe 4 groups. It's a fast-paced enough show with probably the easiest crowd I've ever seen at a comedy show. But its amazing how often the same old things get thrown around with someone mentioning an old bad celebrity as a punchline or a guy going stereotypically gay. You can't really fault the performers when the crowd eats that shit up so readily. The easiest way to a laugh in improv seems to be going extremely silly, which is why a Jack McBrayer or an Andy Daly or Matt Besser are so good because they can do that with either a disarming sweetness or a bitterness that can elevate everything so that it doesn't seem like a trick.
That said, I've only been to improv at the UCB and at its worst, its never been boring or terribly unfunny. That's quite a feat when you look at every other comedy spot in NYC and then realize that comedy around the country is often even worse.
Reading back, this is the most pessimistic way to ever say that most shows at UCB are pretty good.
