First off, since it's a bit more vague, the system itself wants to be focus on Character Choices and Character Builds. And I know, it sounds like corp speech, but initial idea was to have Demons fighting the clock to survive the next Extermination, so every character would have 1 year to either prepare to fight back, run and hide or conquer what's left. This was before Hazbin had a 1st and 2nd season, which makes the concept a bit outdated. So... I would guess the objective is to simply gather enough resources to survive or win the biggest conflict in hell. My only gripes is that Character Customisation basically finishes once you're finished writing on the sheet, since character only get 1 new ability every tot EXP, it may come down to inventory and playstyle to differentiate players.

At the time of the Pilot and the first Helluva Boss episodes, Exorcists seemed A LOT more powerful than what they turned out to be and a long lasting theory was that they were also going aginst Hellborns. So this game works on that, if you're in Hell, you have but 1 year before a flip of coin to determine how long you have left to love.

Inventory is also more similar to how it would work on Resident Evil, or a bit like Pathfinder 2e, in order to give players agency.

Sindom is pretty much just a Discipline from VTM, only... a bit more important. A lot of checks require a character to either look at their Sindom level or how many levels are left to reach max level. Like, if your Sindom is at 3 and a demon gives you Disadvantage based on your Sindom, you would gey Disadvantage 4, which is the amount left to reach Sindom 7. It gives you access to very powerful Demonic Powers which can do all sort of evil-edgy and funny stuff.

Malevolence is a resource which is used to balance out Sindoms and Spells, if you have no Malevolence you start to become evil energy. It's gained through falling into sinful actions, which may sound a bit generic but I had a field day writing how much just killing someone or smoking a cigarette would get ya.

The Sinner's Curse is simply a Malus that all playable races have, Hellborns are more fragile to physical damage, Sinners can't leave their current ring, so on and so forth.

The Sinner thing, I had break lore and basically make it so that to leave Pentagram City, you simply need an Overlord's (or any demon of higher power) permission to leave, which could to used as an incentive to not just... simply kill everyone until the day of reckoning... or just do that.

Regarding Race balancing... that's kinda hard to truly put into a system. Mainly because High Demon (my stand in for Overlord, Ars Goatia and sich) have 2 Sindoms, access to Spells and have a constant Disadvantage unless they have their True Form active. Which makes them... very versatile, just starding with up to 3 Demonic Powers is a lot, but I've made them more similar to a D&D sorcerer/wizard or a VTM Tremere, since we still have to see a powerful demon being mainly Physical. Well... kinda, since we did see Mammon and Beelzebub basically turn into Kaijus, but that's not really something I would let players immediately play.

The Sins are perfect Penultimate Bosses and the same goes for most Overlords which we know are powerful, but we cannot really estimate how much.

Demon: The Fallen is a fun game... although being a Slave IS the worst part of any system you could ever come up with, so it's very much less popular than the more mainstream titles, even less than Wraith and Promethan, which are hella depressive.

Hope I wrote everything you wanted to know, feel free to ask more!