This is a great proof of concept and I'd absolutely love to see it expanded on! In particular I feel there's a lot of potential in the serum creation system, namely the implication that we'll be able to combine serums to create a hybrid mixture and by extension a completely different species.
In that regard I think the best thing to do is to add as many species, biomes and modifiers as possible. I'd love it if stranger, more unorthodox groups of species like bugs, aquatic animals, and potentially even stranger stuff in addition to the standard mammals, avians, etc.
That being said, I think there are some kinks that need to be worked out first. Distendo covered most of what I had a problem with below (especially the lack of ability to save, get rid of test subjects, and lack of bulk serum production/material purchase). I also don't quite know what a good bit of the tags on fully transformed characters are meant to imply besides being useful in contracts. I think if you expanded on this as well it could make for some very interesting gameplay.
I've encountered all of the bugs already mentioned and I trust you'll fix them in time so I won't bother going over them again. The "chicken <NULL>" bug (at least that's what I'm calling it, lmao) in particular is quite annoying as it has the potential to essentially softlock the game by setting research points to <NULL> if observed. The other major bug I noticed is that the "pet shop" biome (and I assume the "canine" species) is completely unavailable even after completing the contract required to unlock it. Whether this is because that section of the game isn't finished yet or because it's a bug is unclear.
All in all I really, really hope you decide to continue development and expand on the concepts offered here. You've built something extremely compelling.