Most of the time it's better to play such a game with one playthrough as a rather good character.

Only if the game is made so that it is not necessary to have experienced all the situations as a good character, it is no problem to play as an evil character.

Because if you play a game absolutely new, the first time and then decide for the evil way, then that is usually associated with hard cuts and miss a lot of content, because you then often get presented many things shortened.

Only when there are 2 fully implemented strands, one for good and one for evil, is it really well implemented.

But it has a very high appeal to play through the first time such a game, first as evil side.

You realize very quickly that in the scenarios you get into you suddenly always have the problem of blowing up the whole store, so to speak, if you are evil and somehow corrupt the storyline itself piece by piece.
This is often because it doesn't have 2 separate strands.

In BG3 it has the grove and the goblin camp at the beginning. But basically you ally yourself first and a little more intense with the emerald grove.
The Goblin Camp, on the other hand, seems a bit more superficial as an evil variant.
But at least you have 2 points of contact, so to speak.

Most of the time it's like this, that you always have one contact point and if you're the bad guy here, then it usually ends in limited expirations.

You kill just about everything and then somewhat lose the actual intended path of the game.

So it would have to be built in such a way that a full 2nd scenario is always available.
So that it for the evil run, from another environment everything arises and the main story from two sides can be played and there are then also always large sections that work differently on both sides.

I have also found that in BG3 initially, that I as quite evil character, was always a little isolated.
If you come to Jaheira, for example, and now basically want to be the evil part, it's going to be hard, because you tend to lack a counterpart.

If you haven't played through the thing as a rather good character at that moment, you're always immediately faced with the problem of having no choice here but either to play along, or to let it escalate and then go a more stripped-down way.

It also became rather quiet in my camps. Because all the rather good people have understandably left. So I stood there with 4 people, until Minthara came to it.
Even Halsin stormed in and wanted revenge and that also still relatively alone. Here one could have expected more, if he already dances.

So what I want to say is that I love it when there is good and evil and you can decide. But then it also needs such an elaboration of both sides that you can play this completely different. But that's a huge effort.