The normal enemies I find bland and predictable. Bosses poses more annoyance to me.
I actually enjoy when a boss is hard to beat(and somewhat not too annoying), it makes the victory MUCH sweeter and MUCH more enjoyable. I find the following annoying but not hard.
Kalle Demos, Moldorm, Gyorg and Morpha.
Kalle Demos was a plant of annoying tentacles, It's hard to land a nice hit before it flips it's tentacles. I hated it's annoyance, but I enjoyed killing it like a weed. Using the boomerang made everything perfect, except when it misses...-__-
Moldorm is just hard to predict, yet the pattern of Killing it is simplicity at it's best. Hit the tail and it takes damage. Easy to see, hard to hit, especially when it goes faster when you try to hit it's tail -__-
Gyorg is a fish begging to be roasted and eaten.
I loved his attacks, but man are his attacks ferocious and annoying. It was SO sweet using Zora Link's Electric barrier to stun and attack it. I loved my chopped sushi at the end of the match.
Morpha is just plain annoying to hit. It's weakness is very obvious, but it's hard to get it out of it's water body. And I really hated his tentacles trying to reach for me, I ain't a stress ball. After killing that thin I was REALLY glad that I won't deal with that beast for the rest of the game, but there is a part of me that say's "Let's go again!"