Alright, so the first thing that immediately stuck out to me was that this manga is very cheesy and isn't really afraid to hold back. That can be a good or bad thing depending on the reader, but for some who are used to the shounen genre, it comes across as pretty tiring and unoriginal. For example, the main theme was uniting all the animals so that they wouldn't eat each other, and anyone who has any decent idea on how biology/ecology works can see how silly this idea is. I can understand what the author was going for, but it's still a naive conflict at best. Then again, I suppose I can't complain for being too scientifically unrealistic, and it's a theme that does make a bit more sense to have when you give animals anthropomorphic features. Overall, I didn't like it.

Two, I'm sort of torn on the addition of the tanukis. On one hand, I dislike them compared to the other animals considering they're the odd ones out. They aren't real animals, and they seem like they were put in the manga in order to replace humans and were given anthropomorphic features to reflect that. On the other hand, I feel like it would've been weird if Taro was given to any other animal species. Maybe putting Taro with the odd species was the right decision? I dunno.

I was originally going to write a bit more about other stuff, but I'm just going to skip to my main problem with the manga.
What made this manga incredibly fascinating and fun to read was watching Taro learn more about the animals and world around him. It felt like a tribal version of Silver Spoon at some points. The theme of self-discovery (as unrealistic and deus ex machina some of those discoveries were) was very charming, and some of the best moments were when Taro first met the elephant or when he made it to the ocean. It was like re-discovering the earth again, and I'm surprised at how well this manga was able to pull it off.

Now I realize that the manga needed to have some sort of conflict, so I understand why the author introduced characters like Giller Giller and Jyu. The theme of exploration and self-discovery could only go so far, and you can't exactly ignore how Taro got there in the first place. That being said, Raiku (author) went bat-shit crazy once he started altering the theme of the story. I didn't necessarily mind Jyu all that much, since he represented the antithesis of Taro, discovering the more violent elements of the world. When he was first introduced, he became one of my favorite characters (Taro was still my favorite at the time). However, when Giller Giller was introduced, that's when everything started to change. At first, he seemed to fit in with the story. Jyu was more of a chaotic neutral than he was a villain, but Giller Giller actually seemed like a true villain.

However, once the plot started to move into the Tower of Babel and chimera portions, I became pretty sick and tired of the manga. The primary charm of the manga was re-discovering animals and how they might communicate with humans given a common language. The chimera were pretty much as far from animals as you can get. After being introduced to a brilliant antagonist like Jyu and teased with what might be a more calculated, threatening villain who could abuse the idea of a common language, we were instead thrown headfirst into some real supernatural bullshit. At this point, the manga started to shift more to the humans than with the other animals. For example, the tanuki and Kurokagi were pretty much given pretty small and minor roles in the last arc of the manga. Even Monoko was given a small role post-first timeskip and before her death, someone who was quite literally one of the main characters of the pre-time skips.
I appreciate the fact that Raiku tried to explain Taro's origins since I couldn't possibly understand how he would be able to after reading the first few chapters, but it's painfully obvious that whatever he had in mind in the first chapter (if he even knew what he was doing) and what he ended up writing in the end was completely different. I could go on a separate paragraph explaining why, but I'll just leave it as this for now.
As the manga dragged on, it seemed less to do with animals and more to do with science and humans, which I honestly think is the exact opposite of how Raiku designed the original story. Animals in the ending arc seemed more like soulless weapons than they felt like actual living beings, and even a few chimeras were given more characterization and focus as the story approached its final chapters. And don't even get me started on the battle between Jyu and Giller. The introduction of random science was so offensively different from the original plot that I almost convinced myself to stop reading right then and there.
This is essentially the main issue with the manga. What you got in the beginning and what you got in the end was so incredibly different. There's no sense of consistency in anything really. Being different from what the manga originally set itself out to be isn't necessarily a bad thing: sometimes you may end up expressing an even better story than what you originally had (ex. Katekyo Hitman Reborn). In Doubutsu's case, I think the change hurt more than it helped it. It was inevitable since going down the same route would have eventually dragged on and left open some pretty massive plot holes, but it doesn't excuse how absurdly different Raiku changed the story. I suppose if you liked what it turned it than Doubutsu doesn't seem so bad, but if you were initially attracted to what it had to offer, the ending arc was a massive disappointment.
Speaking of plot holes, there are a crazy amount of them still, but I don't really feel like harping on them too much since it's pretty clear that Doubutsu wasn't trying to craft a very efficient and complex story in the first place.

I realize I've been shitting on Doubutsu this entire time, but as much as I disliked the ending and a majority of the story as a whole, I still think I appreciate what it tried to do, and I did enjoy what it brought/attempted to bring to the table (I don't usually finish manga I hate). One thing that I'm happy about is that Doubutsu didn't drag on forever. There were plenty of opportunities where Raiku could have dragged on the story excruciatingly long, so I'm happy that he never made the story go completely static (aside from maybe the first 10 chapters). The manga, while incredibly cheesy, still had its heartfelt moments, and I think that Raiku did a fantastic job giving these animals humanistic features. It's also very difficult to consistently draw animals well which was an element of the art I was constantly impressed by.

There are lots more things I like and especially dislike about Doubutsu, but I think I said everything I wanted to say. Overall, it was a nice, fresh experience because it was pretty different as far as shounen manga go. It definitely had its fair share of problems though. I liked Gash Bell far better, and I still think that's Raiku's best work.
I'd give Doubutsu around 6/10 or 5.5/10. Thanks for sharing it with me though, I like reading the occasional obscure manga.

Kinda sad that I stopped at the part where Mayushii kept dying over and over again and in different ways every time. There's only so much a person has to suffer, I'm surprised Ookabe didn't go full on bat shit crazy after so many attempts.