I think well-funded, modern zoos are great! I see lots of comments about exhibit space. Good zoos try their best to mimic an animal's natural surroundings. Though an exhibit may seem small to a visitor, they may not realize an animal may also have off-exhibit space and other holdings that are much larger. They are only on exhibit eight hours a day. For that short period of time, they are shifted into an exhibit where visitors can get a chance to learn about these animals and experience their amazingness.
Modern zoos also support conservation locally and globally. Modern zoos that have undergone the rigorous inspections of the AZA ((Association of Zoos and Aquariums) are strongly encouraged to give at least 3 percent of their annual earnings to support conservation.
Zookeepers are also well educated and are constantly learning the best husbandry practices for the animals they are responsible. A zookeeper is a very competitive job and the best applicant is selected for a job, often competing with hundreds of other individuals. Those individuals often have degrees, sometimes masters or a Phd, and a wealth of experience and knowledge they can bring to their new job. Zookeepers are very hard-working and educated.
I also find it important to exhibit endangered animals and those that are not endangered. Captive care of these animals can provide zoos with opportunities for staff and guests to learn about an animal's biology and perhaps find ways to conserve the species before they become a threatened species.
It is a shame we have kept animals in zoos for thousands of years, but the practice of removing animals from the wild for exhibiting no longer exists, unless in special cases such as orphaned animals or other medical reasons where they cannot take care of themselves in the wild. Most zoo animals were born in zoos, as were most of their parents. It is now their job to serve as animal ambassadors for their species and show their majesty to the visiting zoo patrons, in efforts to encourage zoo guests to be inspired to support conservation and sustainability in their own way. And the best way to show your support is to simply visit your local AZA accredited zoo, pay your admission, respect the animals and learn!