The Glass Nickel seems to be one of the more common pizza places around here, in that if I were going to a friend's place and they were getting pizza, I'd probably guess that they were getting it from the Glass Nickel. I'd say it's slightly better than your average Madison pizza. But, the average Madison pizza isn't particularly good in my opinion.
There are a couple pizzas from Glass Nickel that are pretty good. The Santa Fe is my favorite. Barbeque sauce, onion, cilantro... if you like cilantro, definitely worth trying. Chicken alfredo is another one that's worth trying.
But overall, I can't get excited about it. Their "traditional" topping pizzas aren't as good as some of their more unusual ones, and a lot of the time that I'm getting a pizza, I want a traditional topping pizza. I almost always end up getting something else for dinner when I think about ordering a Glass Nickel pizza.