(spoilers)
The game right now does some things in regards to 'evil' quite well. The evil characters are pretty charismatic and likeable IMO, and the game is occasionally quite creative and extensive in regards to how nasty you can be resolving quests and dialogues. (they put a *lot* of work into things that can happen to Alfiria's lute, for instance). It's great at 'petty evil' sort of stuff. There are lots of great ways to play evil on the small-scale level. It's when it gets scaled up to the main story questlines that it really falls apart, IMO.
The underwhelming and uneven distribution of rewards is something that comes up a lot in critiques of how Larian has handled evil playthroughs. I don't think this is even disputable at this point after the Grymforge patch-the disparity holds true across the board.
You get locked out of three romances by helping the goblins, while only Minthara(more on her later)-by far the least developed romance so far-is exclusive to helping the goblins. This is even without the three remaining origin characters we know are going to be added, and we know are going to be good-aligned. It seems like Larian is fine with making evil players lose half their party members in at one if they resolve the earliest main story event in an evil way, but doesn't feel like good playthroughs should have consequences for their choices.
Then there's how Larian handled the idea of the player siding with the Shadow druids-or rather didn't. Despite the patch that added druids giving unique content to druid characters and giving new quest rewards for helping the refugees and druids, you still can't actually side with them, even if you are playing a druid yourself. It even has dialogue options where you can sympathize with them and another where you can ask to join them, but you get shut down by the shadow druids abruptly and then have to awkwardly shift gears mid-conversation to morally browbeating Kahga into doign the right thing seconds after you were willing to turn on everyone. The process of throwing the tieflings out of the grove is still very lacking (Zevlor tries to kill you, you tell Kahga he's dead, she asks you to finish the job, but nobody else even notices Zevlor's death, you get no rewards for doing it, no closer to your goal of the cure, and lock yourself out of both the evil and good paths, and the romance scenes) It feels like janky unfinished or cut content right now.
And of course the narrative flow of the major good vs evil narrative choices we have so far just isn't as natural or satisfying as it could be- Every patch so far seems to add more reasons to avoid helping the goblins. The new scene with Shadowheart's box, the dialogue options in the temple of Selune where companions point out that the True Souls are brainwashed and that your fate was likely to be the same, and really drawing connection to the mindflayer-cult connection that was already the big obvious reason to avoid the cult. There just aren't many good reasons to join, and your companions aren't exactly lining up to offer support for helping them. Even Asterion, who is the closest the game comes to an advocate for helping the goblins, really doesn't care who you side with.
As an extension of the narrative reasons not to play evil, non-item rewards are also very skewed in favor of those who complete quests in a good manner as well. Right now you can collect several titles and allies-some of whom will continue to journey with you as 'camp followers', but outside of the owlbear & dog pets, these are tied to good choices in the main quests-and even the pets will be upset with you if you help the goblins and use magic to speak with them.
The most recent patch added Grymforge, and unfortunately only seems to have added to these trends. You get several magic items for killing Nere, and nothing for helping him. You gain the Myconids and Gnomes as allies for killing him, and Barcus as a camp follower, while if you are evil you can get the Order of Soul Spiders as potential allies against the absolute, but only as a drow and only if you sided *against* the goblins and killed Minthara prior to meeting him-and only if you mention that you killed her after helping Nere (what?!?)
