I think it all depends on where you live and what Zoos you visit most often. The Indy Zoo is definitely a nice Zoo, but I've also been to bigger and better ones. I live just outside of Indy, so we visit the Indy Zoo a few times per year. We went a few weeks ago and really enjoyed the lights. I have younger kids, so they loved meeting Santa and participating in the other holiday activities. There is construction going on towards the front of the Zoo but you can easily navigate around it.
If the weather isn't ideal for the Zoo and you've got kids, I highly recommend the Children's Museum. They've got some really great exhibits this year!