(Un?)Fortunately I have Ninja Gaiden experience, so only the halfway boss was hard for me, and even that only because I didn't restock on healing, while the rest of the game was pretty much hitting bullet sponges until they finally die, because I didn't do any side quests nor grind. One enemy was 20 levels above me and took like 5 minutes to destroy while instakilling me. Only needed 15-20 minutes in total to get through that one.