It's very subjective. I really like mine, but I find that I don't use it very often because the dies are kind of expensive, and I'm the kind of person who (usually) only makes a quilt once, then I move on to other designs. I have basic dies, such as triangles, circles, squares, jelly-roll-like strips, etc.; shapes I can adapt to multiple designs.
Having said that, it IS really helpful for people who have difficulties using rotary cutters or scissors for whatever reason. Cutting isn't my favorite part of quilting, so I like that it's a little faster with the Go.
Some people don't like the fabric "waste" that they get, but I find that if I plan accordingly and cut my yardage into chunks before I put it through the Go, I get maybe 1/4" to 1/2" waste around the shapes, and I'm okay with that.