First of all I would like to say that I welcome all discussion that isn't fueled by some toxicity and mean spirited comments! :)
So I have been playing this mod rather relentlessly (most my characters are at least lvl 50) over the past two weeks and I'm loving the more game changing features of the skill trees for the characters like Eve (some have less mechanically changing aspects but it is after all still in beta).

However something I really do not understand the point of is the star jewel system. It is clearly meant to only be a way to increase the difficulty of your playtime which is fine by itself but to me there has to be some reward or incentive to do so and well there is no reward associated with using these jewels. The upside you get from using jewels are an increase to exp gain, which by any sizable amount of playtime becomes rather useless. A lot of characters will be close to their full upgrades by the time you feel like investing points into the star tree and low leveled characters will either be too weak to use any substantial amount of these nerfs to your run or would be just fine running it normally as exp gain isn't low to begin with (you can usually squeeze out 20-30 levels on your first run).

I wish this system had a different way of rewarding the player for picking up a challenge. The ancient gems, which actually changes the game quite a bit and they are rather difficult if you ignore working against the changes, do feel fun but there isn't much incentive to ever use them. Most of the basic jewels are very boring like "-1 dmg and 7% more heart scarcity", not very exciting. I might be alone in thinking this but I do not appreciate difficulty increases in games with no impactful advantage associated with it. An idea would perhaps be that you have to use a certain amount of jewels (corresponding to an amount of starmight cap) to unlock a separate skill tree point system with other perhaps curse related changes to isaac (starcursed is the update name after all). Giving a more end game feeling to this mod might be a way to change these jewels for the better.

I'm curious as to what other players think who have dabbled in the jewels or just the game as a whole, I think the system explains itself even if you haven't tried it. :)