How I operate: I play the game normally. But the second I notice something I think is wrong, I investigate. The reason I found anything is because I noticed the sword swinging stopped me while running, but only sometimes. This is the kind of thing that makes players feel the controls are wrong, even if that doesn't necessarily make them smell blood in the water.
If I find out something happens inconsistently, I will then try to find out why on the design level and then the logic level. And then I'll think about if they match. And if they do match, it wasn't actually wrong and I've learned something. If they don't, it's a bug and I may as well tell the developer. They can then tell me why they did what they did if it's not a bug, and I probably still learn something.
It slows you while cutting/throwing.
It doesn't consistently, though. Or I'd have "got" what you were going for and not pointed it out. The logic and design would match in my mind.
If you just hold right and press B it doesn't slow you down. It's when you hold right, release right, then press B that it happens.
If you want it to slow down, that's a bug, and if you don't want it to slow down, that other thing is a bug.

There's the game at half speed so it's easy to see. Something displayed in that gif is probably a bug. Or if you want it inconsistent in this way, then I think it might be bad design.
If swinging the sword without left or right just zeroed out my speed
outright (as in I didn't continue to move after the swing was over), I would have thought it was a game mechanic and not a bug. I promise, I try to think about things before I post bugs.
In what circumstance do I need to hold down while jumping, and THEN also add L or R?
I think that's the wrong question. Why
shouldn't it work when I do?! Say I do hold down, and then press B, and then hold A to buffer a jump. And say I release down slightly after that jump begins. This means I've been scammed out of jump control for some frames
and there's no reason for it. To me this is like asking, "Why would the player want to pause when they're sliding?" Even if they
never would on purpose, there's no reason it shouldn't work. Is the only reason that you don't want to program it? Think about what that says. This is a game you want to
sell, right?
Your game seems to expect perfectly clean input, but that's not how players play. There will absolutely be times where a player will end up holding down during jump for some reason, and they'll feel something is wrong, even if they don't quite know why.
Have you ever accidentally pressed a diagonal in a game? I have. Your game makes me stop moving, then, in a way that's unexpected. If you had some mechanic where my accidental diagonal did something, okay. But you don't, and that's why I'm saying there's
there's no reason for it.
Your game does not seem to handle "dirty" well. And while it's much more likely someone will release right before pressing B, holding down while jumping is a really similar problem. People aren't TASbot. You should have leeway for "dirty" input.
It ignores L/R input while pressing down (to avoid where he's ducking, but also moving L/R)
So does Super Mario Bros. But not in the air.
So does Kirby's Adventure. But not in the air.
So do lots of games, not in the air.
As far as controls, I think your character moves WAY too fast to react to what's coming up. Your character moves at 5 pixels per frame. (I think) There are 113 pixels in front of your character's eyes. This is 22 frames to see and react to something on screen. But in practical terms, it's less than this. If an enemy is also moving toward me like the hedgehogs tend to, it will hit me even sooner. Consider a player that doesn't know the exact level layouts as you do because you made the game. Could they react, or do they have to get hit a lot to memorize what's ahead for their second play? Edit: Possible I'm wrong about how many pixels he's moving per frame, but regardless it definitely feels too fast to react to things.
X acceleration seems uneven. Like I accelerate with a fixed value for some frames, and then get a HUGE BOOST right at the end. This huge boost frequently ends up getting me hit. I'm planning for the consistent acceleration, but that last boost just pushes me into stuff.