They Breathe is a rather interesting specimen. Primarily because it's a horror game starring a cute defenseless frog--not the sort of thing you see popping up on Steam everyday. It's not your typical horror game, either. No jump scares... no "scares" in the traditional sense. Just a subtle feeling of dread and maybe one or two dark revelations.
It's actually quite a good little horror game. Not frightening, per se, but it does manage to be unsettling. Enemies strike a nice balance between grotesque and comical, the watery environment is atmospheric and becomes gradually more menacing as the game progresses, and the whole experience is nicely-paced and doesn't outstay its welcome. Visuals and music are both adequate--not amazing--and do their respective jobs well enough.
The one big issue I have is that They Breathe just isn't very fun or engaging. As a cute defenseless frog, you deal with enemies by avoiding them, or by tricking them into taking damage from other sources. While it does a fairly good job of coming up with ways to vary its basic mechanics, there's little getting around the fact that They Breathe is a game of swimming around, and nothing more. Swimming around a very small screen, in encounters that feel increasingly messy. The whole time, I just felt like I was jumping through irritating hoops to progress. I suspect a lot of this has to do with personal preference more than anything. It plays a lot like an arcade game. Like something you'd find on Newgrounds, or some long-forgotten Atari game. If you enjoy that style of gameplay, you might enjoy the experience. Personally, I just found it dull.
There's very little else to say. They Breathe is a very simple game, and I think it does what it sets out to do fairly well. It's nice to see a horror game that understands "horror" as more than just jump scares and chase scenes, too. But unfortunately, I found the "game" part unengaging. And ultimately, if a game isn't fun to interact with, the other parts aren't going to do much to help.