I'm not going to comment much on the subject both because one can find countless "debates" on this subject elsewhere on the forum and because I think everyone who's responded has summed things up perfectly.
In particular, I want to emphasize what
@Julio C Castro has observed. Everyone who criticizes Bronx's lack of development (while often ignoring any and all projects they have done since Madagascar!, choosing instead to pretend the zoo has been in a completely stagnant state since either 2008, 2009, or 2012 depending on who you're talking to) likes to bring up the developments at the other major US collections for comparison. What people ignore, though, is why those developments are necessary. Zoos like San Diego, Omaha, and St. Louis have been pushing their remodels and developments in part due to the fact that what was there originally is just plain bad. Compare that to Bronx, where yards constructed in the 1940's are still standing and still better than what most zoos' new developments for the same species are. Why would they zoo tear down perfectly great habitats to build new ones that just look flashier?
I do agree that some of the zoo has been looking a bit run down as of late, but that's why their constant renovations and redevelopment of older areas should be highlighted. They have done a great job of maintaining what they have and I've actually been very surprised to see just how much they've pushed forward with necessary renovations through COVID. I really do think part of the issue here is that Bronx doesn't exactly "feel" like a US megazoo in its design. Most major US zoos are significantly younger and consist of exhibitry styles following modern trends in America, ie. a relentless amount of mockrock, "grotto-style" hoofstock yards (if they choose to keep hoofstock at all), and grandiose visitor viewing areas. And genuinely I'm not saying those are inherently bad or that they're worse than what Bronx does. They're not worse, they're just different styles and are done in a different way. Bronx on the other hand is a very old zoo for this country, it will be celebrating its 123rd birthday this year. It was by and large designed in a style akin to that of the older Central European zoos. For those more used to younger collections, the older look and feel might not be as appealing, and that's okay. It doesn't make the zoo bad, though.
This isn't all to say there aren't criticisms of the zoo either, though. I personally find their signage issues really awful nowadays, though on my last visit all the signage in World of Birds had been replaced and I know they have made updates to the JW signage so hopefully this is an issue being actively resolved.
Claiming all the zoo has done since Madagascar! is phase-out animals, close exhibits, and not look into the future is absurd, however. The 2009 budget cuts were hard on the zoo and clearly they have had a lasting impact combined with NYC's soaring construction costs and the utter destruction of the NY Aquarium for which the WCS is also responsible for. That said, since at least 2014, I've only seen the collection continue to grow. Despite the only larger developments at the zoo since 2010's being the new Komodo Dragon/giant tortoise exhibit and the remodel of the Children's Zoo, the zoo's collection has grown steadily. New and unique herptiles are being added all the time and the bird collection has grown by at least 1-2 dozen species since the new curator took over. The small mammal collection has perhaps been hurt the most but that's just due to the general lack of interest in small mammals in the US and the fact that many of these species have short lifespans. Currently, the Mouse House collection has dwindled slightly, but just as has happened in the past I suspect it won't be too long before they find additional species to bring back in (they've already added Feathertail Glider and Barbary Striped Grass Mouse, for instance). The Asian hoofstock collection remains phenomenal despite them being pretty alone in breeding quite a few of those species. Their Gaur herd has never been larger in the time I've been visiting the zoo, and they have new breeding males for several of their deer species. Not to mention the addition of Bactrian Deer, which is a huge win especially since San Diego seems to no longer have an interest in their deer.
This is longer than I intended already so I'm going to cut it here, but in essence I think if people want to criticize the zoo they should find some more accurate material. These same arguments are almost older than some of the members making them

At least that weather/climate arguments seems to have been firmly put to bed.
~Thylo