I love deer and when I saw the park was free I thought I would give it a go. It is located in the Lake Gardens (10RM taxi from KLCC) and just a few minutes walk from the big Bird Park there.
There were maybe 20 deer in a reasonable sized enclosure with shaded areas for them and us to escape the heat. It was such a hot day the deer weren't moving around much.
There are also monkeys roaming around, we got some great footage of a couple of them swimming in the creek.
The mouse deer are in separate, smaller cages like a zoo. They look a bit like rats. I was a bit disappointed as I had hoped they would be running free too.
Overall I wouldn't bother going just for the deer park but it is free so it's definitely worth stopping by on a day out to the Lake Gardens.