Anyone going back to try out ZT2, really needs to install
Radical Remake - it fixes the ugly ui, adds a bunch of amazing model edits/retextures/variants and fixed a lot of issue with the game in general. You'd probably also want a hack to allow you to place scenery items off the grid, so the placement limitations don't drive you insane. I wouldn't dream of touching vanilla ZT2, as it's just way past its sell by date at this stage. I would imagine when most people think back fondly of ZT2 they're thinking of RR - I've played it recently and it still holds up incredibly well for such an old game. Sadly, it's reached the limits of how much you can mod such an old game engine before it just breaks, which is why a lot of people moved on.
I was still playing up through like, 2016 or so when it stopped working via Crossover on my iMac. I bought a new laptop this year because said-iMac was on the outs, anyway, and Planet Zoo was in the wings...
I had all of those mod installed, including Radical Remake. It holds up well, all things considered but I just can't go back to it after playing Planet Zoo. The building just feels way too limited as far as the exhibits are concerned with Planet Zoo in the mix.
But all of the animal options... Those are still amazing, and frankly, kind of messing with my expectations. Haha.
On the topic of PZ plants? I hate the entire system with a passion. Firstly, the continent matching system is dumb and unrealistic - just limits enclosure design for no good reason. ZT2 foliage was amazing. You know why? Because they let people mod and the community produced an amazing variety of plants to fill in the gaps. Almost anything you could want was available, and if it wasn't you could add them yourself, or request for someone to make them for you. Sure, the plants in PZ look great but there's just so little choice; I'm not sure they'll ever add enough plants in DLC to satisfy me (especially if they don't remove the daft continental restrictions).
The "continent matching system" is annoying in terms of keeping animals happy, but... I like the design of almost all the plans in Planet Zoo. Even the modded plants in ZT2 were very rarely satisfying for me to plop down. I just can't get beyond the graphics with the way most of the bushes looked. Trees were fine, but the bushes and smaller pieces always bugged me. But that's a preference/taste thing.
I think adding more foliage as time goes on will help the variety, as would updating the continent restrictions. TBH, I would prefer they adjust that to be biome-specific and then have a list of "suggested" plants/foliage for a given animal that will increase happiness beyond a certain threshold (for example, they could be fairly happy with foliage from a similar biome but you might only be able to hit 90% or so at a max--but if you include the suggested plants it would allow them to hit 100%).
PZ will be a good game when they iron out the bugs/QoL issues, but I don't know if it will ever be a truly great game without the help of the modding community.
For me, as far as the modding is concerned, what really helped ZT2 was the flexibility provided by all of the additional building pieces and the inspiration that having access to a much wider pool of animals allowed. And many of them were fantastically developed!
I actually get why they wouldn't want to open things up and actively support modding quite yet because they would rather people pay for DLC. This makes perfect sense to me for the time being. I kinda hope they change their tune on it after the game has run its course, but that is a way's away. They did release that Thememaker's ToolKit that allowed people to develop new scenery items. Not sure that they would do something like that with Planet Zoo -- and if they did, I'm not so sure that animals would be feasible (in fact, I kinda doubt it). But that blows things wide open if they can. Because then it's a community effort--and not just the group of developers at Frontier.
And animals are, for me anyway, what really inspire me. "Oh, I'll create a section of my zoo dedicated to these animals!" The shape and form of the exhibit for that animal is what drives the way everything looks around it. So adding more animals will inspire more creativity, etc.