If you really don't enjoy it then I can't get you to finish it, but I can give you a few suggestions maybe.
- The mana regeneration: Yes, you probably chose the "wrong" birthsign, though if you did, it is still one of the strongest in the game, and the "no mana regen" is basically meant to counter its advantages. And that means you can't regenerate it at all, because without mods, you can only regenerate Mana when sleeping if you not chose this sign. But there are ways to get your hands on potions other than completing quests. Alchemists sell them, and you should find one in every mages guild and every town, though they have different qualities and quantities. But for example Nalcarya of White Haven in Balmora (has her own shop) sells unlimited potions of the highest quality, including restore health, fatigue, and magicka. She only seems to have one or two of each, but they should restock every time you talk to her. Another way is using alchemy to make them yourself. At first you only see one or two alchemy properties per ingredient, but as your skill increases you unlock them all. Combine two ingredients with the same property (using alchemy apparatuses, preferably of high quality) to make a potion with this property. Also, you can just use the raw ingredients on your character to get the first effect (though weaker than in a potion) and raise your alchemy skill (though slower than by brewing potions).
-The walking/running thing is really annoying, especially in the beginning. Potions can also help you to keep your stamina up, or you could use a mod that reduces or removes stamina loss when running.
-The assassins are a real problem. They were added by the Tribunal expansion and the implementation is really bad and effectually spoils the beginning of the game. I highly recommend using a mod to delay the assassin attacks to a higher character level or a later part in the main quest (or even after it).
- If you are followed by a monster and cannot escape try finding a city or village and let the guards handle it. Of course, out in the wilderness this could be difficult. Another possibility would be the Mark and Recall Spells which allow you to mark a point to which you can teleport back any time. Set it in a town before you go out exploring and you can always get back to safety. Even better may be the Divine Intervention and Almsivi Intervention spells, as they teleport you to the nearest temple or tribunal temple.
- I can understand if you want to play the game in its original state, but even though I love it, I don't know if I could ever really play it without mods (the first time I tried, I also quit quite fast, but that was also because I expected something different and didn't know how to play it), because there are just so many great ones out there and the game does have its issues, I don't deny it. Though once you start modding, chances are you will spend more time with it than actually playing the game. And I won't lie, mods can also introduce new problems. But a few here and there to get rid of the most annoying parts... why not?
On topic: I haven't really quit anything this year, yet, but I basically stopped playing Beyond Divinity and don't feel like continuing it any time soon. It is nowhere near as good as Divine Divinity, really.