Hot take but the animal behaviour in Planet Zoo is kind of lacking. I feel like it was more interesting/complex in Zoos Tycoon.
In Planet Zoo animals have great animations mostly triggered by enrichment objects but do little more than wander around, run like crazy for no reason, climbing to random things if they can and sleep.
There is little interactions between the animals and their environment and i would love more of that.
Hotter take.
Because you spend more time building in this game than in Zoo Tycoon 2, you notice much less of the behaviors than before. On top of that, ZT2 also had the benefit of having an animal thoughts panel in which you could read what the animal was doing, which Planet Zoo lacks.
One of the things I loved doing as a ZT2 modder was use the behavior system and implement loads of cool behaviors, so I've seen my fair share of what is included (for instance, the Triceratops introduced night behaviors, where the animals would come together at a specific time at night, something very few people including myself ever actually noticed in the game.) based on the actual TSK and BEH files that defined the behaviors.
Having written an in depth guide on it, I do feel kinda qualified to talk about the behaviors in ZT2 in an objective fashion
With that information in mind... people really tend to have a very nostalgic image of what Zoo Tycoon 2 did, and whilst it did have some really cool behaviors, a lot of it is just people misremembering stuff. Like, I'm sorry to burst the bubble, but there was no behavior that would make the lion roar at an animal in a nearby enclosure. The lion would just roar from time to time, and most likely they roared at an animal in the enclosure itself. There were plenty of cool things, but a lot of it was also pretty basic and appeared a lot more complex as you played it when you were younger.
That said, the one thing I do think that Planet Zoo is missing is indeed
more interaction between environment like marking/sniffing (without triggering it yourself by placing in new items)/scratching. And whilst JWE2 build upon the interaction system that Planet Zoo does have, Planet Zoo does not seem to go that far (which honestly, is okay because some of the interactions in JWE2 are more there just to have them), so I tend to agree that some more interspecies interaction wouldn't hurt either.
But, one thing that I've also noticed and seemingly has been confirmed by other players too; disabling welfare all together seems to heavily impact what the animals do. Enabling welfare and setting the game to hard mode increases the chances of animals showing cool behaviors, so I'd suggest anyone to give that a try. It ain't perfect, and there sure is a lot that is missing, but there's more than most people realize.
