The spearman felt a little weird or unfair at first. Because if you walk up to them from the front they poke you pretty quickly. And their spear animation is kind of hard to notice. But if you learn to get behind their patrolling, then they are a piece of cake to deal with. There are likely many paths to solving this. Some simple solution might be to have the spear shaft thrust in front of the enemy's torso. Looks like it is animated to be behind him almost. Or you could have a longer, more exaggerated wind up. And so on. As I am not the developer, I will leave the creative problem solving to you. That is a lot of the fun of creating a game.
The big brute enemies were good to fight. Felt fair and they telegraphed their attack well.
I have a problem with the ninjas. The first 2 encountered seem to come out of nowhere. As the character runs pretty quickly and the screen is small. So you are sprinting along and suddenly there is a ninja 24 pixels in front of you. And they immediately chuck a shuriken at your face. Perhaps there are people out there who can react that fast. Not me. But the like 3rd ninja you encounter. The 1 you get a first glimpse at from a lower level. Now that felt much better. I was able to realize it was there ahead of time. And plan accordingly. So to me the problem could be viewed from 2 angles: level design or enemy design. Depending on how you envision ninjas as a challenge to overcome. Keeping the current implementation and using them as a "see this ninja here, you better remember they are here when you get to that area". Or whatever other clever uses you can come up with. Or giving them a slight wind up animation or possibly a slower shuriken.
There is some room for argument against most of what I just said. The game does seem to be about one-man-army storming a castle. The character does have quite a big health pool. So even if some of the things I said would normally feel unfair. For this game it might add to the feeling of power the character is supposed to have. Running through these rooms, taking all these wounds, but still charging onward. Comes down to your vision of the player's experience.
Perhaps I went a lil' overboard here. But hopefully it can be of some use.