The Phoenix Desert Botanical Gardens have always looked interesting to me, I think partly because the landscape is so different from where we live.  It is a really cool place, with lots of desert plants all set around half a dozen or so loop trail.

With that said, I don't know that I'd go JUST for the gardens during a regular day.  However, they do plenty of special exhibits like butterflies in spring and open they the gardens at night for a special experience.  But, we went specifically to photograph the Chiluly glass exhibits.  They were REALLY cool lit up at night.  Enjoy!  (Here's the map)