I went here for Las Noches de las Luminarias a little over a week ago (which I think runs through to the end of December) and so I only saw the gardens at night, but it was still a great discovery. They pretty much have different mini-desert-ecosystems placed throughout the garden and with the luminarias lighting up all the pathways at night, the entire place has an even cooler feel to it.
Granted, with this being holiday season, you've got barbershop quartets, bell ringers, and people meandering around drunk on Irish coffee interspersed amongst the countless species of cactus, but beyond that, you've got great walks with several pathways leading you all over the garden.
Definitely will have to come back in daylight sometime.