He whines a lot about it being hard. Even suggesting at one point that it's more difficult than Japanese schmups.
It's really, really not. Even compared to something like Jamestown (a relatively easy schmup), Gungeon is pretty easy. He even goes as far to suggest that certain boss bullet spread patterns are near undodgable, when they're not. When he suggests that he shows a clip of him rolling into Canon Balrog in the corner.
It just seems that he had a really hard time with the game and didn't really 'get it'. To be honest.
Honestly I think some people enjoy this genre because they enjoy the behavioural aspects of game design that stem from the variable reinforcement mechanisms afforded by the heavy reliance on random generation in games like Issac. In that regard they enjoy games like Issac for the same reason that my mother enjoys playing Candy Crush, the idea that with 'one more go' the variables will align and grant me a win. That element of a rogue-lites design has less emphasis in Enter the Gungeon, but that doesn't mean it's bad, unbalanced or too hard, it just means that game expects more from the player in regards to influencing their own success.