Random_Coffee: I have OCD about playing all games on the highest difficulty. I played Ys 8 for 30 hours on nightmare, but got fed up with the grinding. Then I started a new playthrough on hard and got just as far in under 6 hours.. I also quit Ys Origin a few years ago for the same reason, but I will get back to it.
I don't like Ys Origin's Nightmare mode, as it makes one of the game's more interesting features, the ability to get interesting upgrades by spending a special currency, essentially unusable.
There's also the fact that, if you're playing as the third character, the short duration of Boost makes one particular segment earlier in the game potentially incredibly frustrating (I haven't tried it, but it's a part where Boost is required). This is a shame, as the other part where you need to boost, I think, could be quite interesting (HP management when you're constantly taking damage, have a limited (but rechargable) ability to mitigate it, and a nice HP drain ability, sounds like it could actually be quite fun).
There are some other games where the highest difficulty is not reasonable:
* In Paper Sorcerer, the hardest difficulty makes it mandatory to spend some extra time leveling up. (Then again, even on the easiest difficulty, this game lulls you into a sense of security (game becomes too easy), only to then suddenly face you against enemies that can easily wipe out your party.)
* From what I understand, in Cosmic Star Heroine, the hardest difficulty is ridiculous, and the first battle is apparently unwinnable without making use of a mechanic the game doesn't teach you until later; Heroine difficulty (the second highest) is recommended for this game if you like to play on harder difficulties.
dtgreene: I remember playing Shin Megami Tensei: Nocturne on hard difficulty, but ended up quitting for two reasons:
* The combination of instant death attacks used by enemies, the main character's death being instant game over (even if you have another party member with a revive ability), and the fact that you can only save in certain spots and have to reload after each game over.
* The music in that game was giving me headaches.
jepsen1977: Completely agree - I like the SMT/Megaten series but they do have so much BS in them that they seem to have been made with a guide in mind as in using a guide to tell you about upcoming bosses and what strength and weaknesses they have and that's just not fun. But other than that I do like them and do enjoy their difficulty when it's fair.
Bosses like those aren't the problem, particularly if you can realistically change your setup to match the boss, and you can quickly retry the fight when you fail.
It's when regular enemies can easily cause a game over (especially if there's nothing you can do about it), and the game forces you to lose progress when that happens, that it becomes an issue.
(Interestingly, Final Fantasy Mystic Quest can get quite mean with its encounters (just watch speedruns (especially marathons and races) to see what I mean; however, that game, in addition to haveing save anywhere, allows you to retry a bettle if you lose it (especially nice if that happens on the first fight, which comes before the first opportunity to save).)