Here's a few design hindsight. It's not to devalue your feedback at all, it's just that I thought it was interesting to share, and may give you another perspective on what we tried to do with the game.
I feel like getting punched from behind isn't that much of an issue because you can heal a lot. Our combat design was inspired by doom eternal, where you can't really dodge damage but you also heal a lot when glory killing and stuff.
So for this reason I chose to not dedicate too much time to give players ways to avoid damage. Because I wanted to create tense moments when you lose all your life and have to run for it, until you find an opportunity to heal (which requires agression, so there's tension between dodging and attacking)).
With that said I can understand that it may feel bad to get hit without any way to know about it. There are a few things we've identified that could help with that (namely, lack of sound to tell you when an enemy is about to hit / when you get hit, and enemies spawning instantly and often too close to the player). Sometimes you take damage and there was nothing you could've done, it's pretty frustrating. There's a middle point we couldn't find yet.
Also, you're absolutely correct that we could've communicated better on a lot of the mechanics. That's a lesson I've taken from this jam : tutorialize and explain everything, the fun is playing the game anyway.
Your feedback is greatly appreciated, thanks again for sharing.