The intensity is pretty overwhelming. Feeling the vagina stretch to accommodate while tensing up and feeling the warmth of it throughout your body is enough to daze me for a bit. The fisting and punching comparison is definitely good, although not exactly straight forward because it doesn't really feel like a normal punch. I'd say its like being being punched in the stomach, but different, both because it is significantly more powerful than any punch and because it doesn't work like a punch does. I'd say it can also feel sort of like a stomach ache or a cramp, but in a weird way. I generally love and hate questions like this, because its like asking what any kind of touch feels like. At best your can compare to other feelings but it's harder to say how its different. I can't really describe why I don't personally find the pressure and the thrusts uncomfortable, because I really enjoy it. Any time I get to enjoy it, I'm a blissful and mildly shaking wreck, like a hard day at the gym but more enjoyable and comfortable. But at the same time I do get why many others wouldn't.
I do however have the benefit of having friends who are also zoo and are active with their horse or have tried it, so I have an idea of their experience with vaginal. The experience seems very heavily dependent on your body, and how much they've trained and pushed themselves before they started and how they did it once they started. Height and build definitely also factors in obviously, as does the temper and force of the horse. It'll be the difference between enjoying the very stuffy feeling and feeling like you're being bludgeoned apart from inside. For those reading this who are more curious about trying it themselves rather than just horny, definitely make sure that you not only read up on how to do try it safely, but also be honest with yourself and try with toys to see how far your body can go. You need to really understand your limitations and accept them or you'll get hurt, because the forces involved if you take any non-acclimated horse without an idea of how it moves and how your body best fits in front of that movement, you will definitely die.