I was there for two full days in January of this year. It is a mediocre zoo. Monkeys and orangutans are in indoor houses right out of the 1800s. Gorillas were the same during winter when I was there, but it looks like they have a nice large outdoor hillside for warmer weather. You look down on two elephants in a small pit - they need to be shipped out immediately.
The only good parts are new Rocky Mountain trail and Giraffe Ridge. They have the largest giraffe herd of any traditional zoo (somewhere around 20). In warmer weather, there are also some smaller animal exhibits along edge of giraffes (red river hog, etc). Rocky Mountain area has an excellent 2 yard grizzly exhibit, one with a pool with underwater viewing (see my photo of my cousin by swimming bear in the gallery). Four mountain lions in a very uniquely designed exhibit, although a bit too small. Otters, canada lynx, one young moose, procupine round out the area.
There is also a string of four asian cats from cold mountain areas - siberian tiger, amur leopard, pallas cat, snow leopard. Tiger is very good yard, leopard and pallas are ok, snow leopard - which is the newest exhibit - is atrociously small. I don't understand how an AZA accredited zoo could build such an awful exhibit. Maybe because the one up the road at Denver Zoo is even worse!
I went in winter specifically for snow pictures, and I got some good ones. Winter is a good time to visit for that, but downside is some of the warm climate animals are indoors. A summer visit will see most animals, but you will miss the nice scenes of siberian tiger and grizzly bear in snow. I should mention they also have a small mammal house, which still has animals inside, that is now closed to the public, presumably because it is so bad they don't want anyone to see the conditions inside.
BOTTOM LINE - If you're in the area, stop in for a stroll, but I wouldn't make a special trip just to see it.