Short review:
I ride my bike a lot...usually about 100 miles/week. I'm on this particular path every single time (so 5 days/week).
It's beautiful and winds along Lake Mendota. It's functional. If you can put up with the idiots who like to walk on the wrong side of the path, it's a worthwhile ride.
It loses a star for one reason: A lot of the path is in shambles. It hasn't been paved forever and cracks are everywhere. For a city with lots of money to spend and one constantly under construction, you'd think Madison would take a couple weeks to pave the damn thing.
I'll keep riding on it regardless, though.