I agree with others that it seems a bit expensive at $15- but that still would not steer me away from going.
For the first time in about 8 years I found myself at the DBG with some out of town family. Wanting to enjoy the weather (since they had just escaped the cold grey winter of Detroit) the gardens were the perfect spot. The garden is equipped with wide paths and plenty of benches to help the old timers pace themselves. It helps remind us city dwellers of the beauty the desert can have and how unique Phoenix truly is.