This place is AWESOME!!
We went in right as it opened, which is the way to go. It's a little pricey at $19.95, but I think it was definitely worth it. You'll have to make several passes around to see the full spectrum of the butterflies they have (which vary seasonally). You need to be patient, too, as the butterflies won't always open their wings when it's slightly overcast. It's an indoor facility, and fairly humid inside, but the sun shines through. The butterflies will land on you if you stand in the sun and wear a white shirt.
Probably the best part about our experience was that one of our family members studies the butterflies in her free time and ended up giving us an expert tour! Bring a camera and use the guide they give you...it's so fun to identify them! The koi are really cool, too. We even saw some baby quails that hatched only the day before! It's a diverse environment, but it is fairly small. So look for the details! The other must-see is the chrysalis display where you can watch butterflies hatch!
This is one of my very favorite things we did on our Phoenix trip, but go early, or it will be too crowded.