Great coffee, great character, fantastic location (for ASU folks - don't even THINK about trying to park a car here). The food is good, though limited, and I'm not a huge fan of them now outsourcing their baked goods. Service can tend toward a little slow, but I think it's mostly due to a shortage of staff - there's only usually one person working at any given time.
My biggest complaint about 3 Roots (and it's sort of a fake complaint), is that the art usually SUCKS. Amateurish, gaudy, underwhelming in general. I mean, you are right across from the Art Museum, the School of Art and the Schools of Design: get some decent wall fodder.
Doesn't keep me from going there 5 times a week though.