The Singapore Zoo has a great reputation, and for good reason. It isn’t cheap to get in, but for that money you do get a very nicely designed zoo. The zoo also supports various conservation efforts and research projects.
I took these photos on my visit to the zoo a few years ago.
The viewing options were often excellent, like this great view of the lions.
There were several shows in addition to feeding times and talks by wildlife experts. If I remember right these were free (or some were free?).