I was pleasantly surprised. The UI is slick, there are no ads, it does traffic-based redirection, lane guidance (something Waze still doesn't do), lane closure warnings - it's pretty good.
I guess the usual criticism is that the maps are inaccurate but it's really improved over the past year or two. I think the knee-jerk complaints are from people who haven't used it recently.
I appreciate that it's the only major nav app that doesn't constantly record my position in the cloud.