IDK if it's Drinkbox's implementation of 'shield-break' mechanics specifically (I didn't particularly care for them in Guacamelee 1/2), or just shield-breaking as a general concept, but while the game is pretty forgiving overall (and that I can already start seeing pretty OP combo situations), the requirement of switching forms/abilities to shield break (especially when form switching using the hotbar doesn't pause/slow down time, though IIRC you can just do it from the menu) annoys the bajeezus out of me.
I do like that dungeons clearly show you which element(s) is/are needed ahead of time, and it's less of an explicit issue later on once you can start swapping abilities over and using certain passives if need be, but it's just...not fun for me, lol.
I'm on the 3rd gem piece, and while it's fun, I can definitely see the potential issue for repetitiveness, even with the varied quest bars filling up fairly consistently.
Here's my current extremely incomplete tier list, since I've only unlocked some of the classes and then only some of the abilities within them
top: Mermaid
good: Horse, Magician, Slug
okay: Ranger, Knight, Rat
blah: Egg, Nobody
It's funny, because IMO mermaid starts cool, then falls off hard later on - the passive is pretty useless, as you generally either don't want to get hit, or pump out major damage via combining status conditions and the slug passive, and the mermaid's locked skill isn't a full-on rapid hit like the slug unless you actively mash, so generating mana is a bit of an issue to spam skills from other classes, even with her large MP pool.
Ranger needs a bit of a speed boost on her basic arrow firing rate IMO, but I suppose that would risk making the rapid fire ability useless.
Zombie so far is probably my favorite overall, with magician and ghost for certain situations being decent/good. Most of the other classes have bigger drawbacks like having hard(er) to generate mana with their class abilities, or lacking synergistic movement skill options, even with the 'base move can't go below 100' aspect, imo.
Aside from the base class (which...why would one ever use that aside from a hard mode run, lol), I think turtle is the worst - only used it once to unlock the light-damage AOE spell, then haven't even wanted to go back.
Egg is also clearly bad, but is IMO fairly obvious as a dragon quest style 'jester --> sage' requirement for the last class, so it's more forgivable - plus it has a good passive for several quests, and at least one dungeon.
Haven't unlocked the 'A rank' locked classes yet (Monk/robot/rogue) yet, though, or the last one.