Respectable. Sadly, most games are casual nowadays, since you don't want to turn supporters off.
And hard difficulties don't make much difference, since they simply cut your resoures, which doesn't matter when mechanics are primitive.
Anyways, subjectwise. Ranged by decreasing difficulty.
The Fairy, The Succubus, And The Abyss - older than the time itself, this game was initially meant to be a survival horror resource management. And it still is, although by modern standarts I doubt it can make anyone feel scared.
Become Tentacle and
Become Tentacle - later girls, like knights, are rather tough bosses to put down.
A Zombie's Life - borderline, mostly casual and somewhat grindy, but there is possibility to lose by running out of resources and a tough 3 or 4 stages final boss (patient zero).
Urban Demons, Town of Passion, Zombies Retreat, Peasant's Quest, Renryuu: Ascension and whatnot - nice puzzles, nice bossed, need wits sometimes, but using wits is not a challenge, is it now?
There is also a possibility to look at
Cracked Vessel and other games from NearFatal //AGlassOfMilk. They are made to be somewhat difficult in different ways each, and are generally worth their difficulty.