Pretty easy with the Rogue. Going to explain how to beat the hardest difficulty ("Nethack"):
Find enemies that don't damage much and spam "Steal" on them to pump up your gold. If the amount of gold you steal is close to the damage the enemy dishes out, that's a jackpot (potions heal more than double what they cost).
On "Nethack" difficulty it can take a couple tries because you may get unlucky and never reach a potion seller, or keep getting hard enemies, but still not that hard. Just manage your potions and health and keep yourself out of danger. Use leveling up as a way to heal instead of wasting a potion. Don't stay in the first level too long, eventually level 1 monsters get harder than 2nd level monsters and give little experience. Mushroom, skeleton, and ghost enemies are great to steal from in the beginning.
The real trick is to buy a "gas can" from the "Dictator" in level 1. When you run into the "crowd" enemy with the gas can, they won't be able to hit you. So you can spam "Steal" and get 100's of gold while taking little to no damage. Same goes for buying an "Anti-Kube" from chef behind the red Kube in the first level, Kube enemy can't hurt you. And same goes for buying an axe from the lumberjack girl, and fighting a tree monster in the second level. 3rd level was easy pickings after that, even on hardest difficulty.
I almost always use Counter, and then stab. I was able to kill all the "gods" in 3 hits or less. I also used "Krillix" offers a lot, to trade in a lot of that DEX for PWR.
I liked the game a lot, especially considering it was made over 5 years ago. Other characters make it more challenging, so that's good too.