As someone who's a massive fan of The Binding of Isaac I'm very biased when I say that I think your game is great.
You have a really nice variety of content for a jam game in terms of the enemies/items/bosses. You even have different room layouts.
As far as the difficulty goes, I always had to work to stay alive and I could never relax in that OP way you can in Isaac, but I also won 2 runs out of 3. (I'm not counting the run where it gave me the boss straight after my first item though, so my health wasn't full.) Personally I think the difficulty feels pretty good right now, if not a smidge in the player's favour.
In short: excellent.