Really loved the game. Would like to definitely echo what other people have said with really liking the planning and decision making you have to do for a run. I felt the leveling up process to be really neat and choosing items to be quite a fun process. Enemies and combats started slow, but really ramped up with what they did, and I liked the difficulty curve a lot.
In regards to feedback, I struggled a bit understanding when an item I could pick could only be equipped on certain heroes (before choosing them, of course.) Also, I had no idea what the one "if this saves an ally, go again" really did. I think it didn't explain on hover text, and didn't specify that it allows use of the exact same action again.
I also found myself clicking on the die themselves instead of the hero's portrait to view their die... a lot. It took me awhile to figure out where to go to view the die while in combat.
I also didn't really know about the ? menu at the top, and reading through that is probably something that should also be accessible from the title screen (it might, I didn't notice it.) It helps clear things up a lot, but I can also see how having it while the game is being shown is probably necessary for understanding.
I really liked the +X number when your hero is taking fatal damage. It helps a lot. I found I REALLY liked the "special hearts" enemies have that have a special trigger occur on them taking that damage. I feel that makes fights incredibly unique. I also didn't really know what "retreat to the back" meant, I assumed from the wording it would cancel their ability (although I don't feel it should now that I've played the game through) - so explicitly stating that they just move to the back might be helpful.
Finally the last thing is that I felt each hero's archetype was really unique and well defined. I would almost like to see this taken further and minimizing the amount of overlap of abilities, but so far I think it's done quite well.
Great game! I look forward to the paid version and all the extra content that comes with it!