Huh, some people are having quite a bit of trouble with this game... Granted, it has quite a few quirks to it that aren't necessarily well explained... Some don't seem to be explained at all.
That said, maybe I'm just getting old, but this thing has a pretty standard game-loop for an RPG... Go in the Labyrinth, farm for as long as you can, retreat and do some stuff outside, rest, rinse and repeat many times... The fact that there's an obvious limit on stuff like fishing, the duration of the lottery events and the need to pass a day for certain quests to update make it obvious that you're supposed to take multiple in-game days to get anywhere. This is further emphasized by day-long buffs like the Torch buff and the luck buff.
Basically, it's intended to get people to use a lot of time to get anywhere, so to speak, and also create that illusion of working hard for results... and ultimately, you DO get results if you keep at it and figure out the quirks of the classes and the combat system in general.
Once you do, and once you have some levels on your characters and the Audragon sword, you can farm virtually indefinitely, but it does take time to get there.
Personally, I'm running Main-Character Mage, though I intended to dip into the other classes for some of their passives eventually. Torte is my Warrior, specced with sword and board and some crystals to boost Hatred generation... not that most things live long enough to hit her much outside of bosses. Fano is my hunter, there to clean-up or auto-attack easy packs, and she also carries the crystal that reveals elemental weaknesses. I multi-classed both into Mage up to level 13, to give them Mage Shield and Meditation, both of which improve survivability as well as run-length if I feel like it.
Currently, I can run level eight farming sessions for virtually forever without running out, with only some occasional healing potion usage as long as I'm patient.
The key to that is honestly the element system. Figuring out the right weapon for your Hunter for each level, as well as figuring out which elements to boost for both offence or defense is the main key for success.
I'll also add that most auto-skill gems are useless. The ones I did find useful are the one that clears debuffs, the sleep one for most levels though it doesn't seem to work much any more around level eight, and the two that buff either magic or attack at the start of battle for that sweet Alpha Strike potential. Still, you have to be careful about that since you DO want to extend some fights to slip in Meditation.
For the other types of Gems... well, I'd never use the ones that lower Agi. Turn speed is all determined by Agi, so lower Agi means lower actions. Get it low enough and enemies will literally run circles around your characters.
Regardless, I'm finding the game fairly fun, even if the hentai content is mediocre at best. It's a nice time-waster while I also do other things.