I'll preface this by saying, hi, hey, I'm an EA player, which is gonna colour my views a bit

I don't find the Emperor or his storyline very engaging. As the Dream Guardian, his schtick of "I'm protecting you but I have secrets that I'm very obviously keeping from you" genuinely less interesting than the outright predatory seduction Daisy had. And the funnier thing is, in Larian's attempt to make the Guardian (and by extension the tadpole powers) seemingly more trustworthy and a more tantalizing option, they kind of failed. I ended up not trusting either, but with Daisy at least, I was invested and curious on what their angle was. With the Dream Guardian, it felt obvious that there was a shoe waiting to drop, which leads into...

The Emperor themself. It's probably more due to late in development rewrites, but the story kind of grinds to a halt when he's introduced, with his fancy cutscene monologue about his backstory and lore importance. It feels less like an organic plot beat and more like playing catch-up with the rewrites.

I don't think he's poorly written, there is some merit to the idea on whether having the memories of his previous life means he is still who he was. But I don't think that's explored as well as it could be, and Larian plays a bit fast and loose with it later with regards to Karlach and Orpheus. And I think that, with the revelation on what group he was a part of when he was roaming Baldur's Gate, and his enthralling and use of Stelmane, his threats to do the same to you, make him far less of an alluring option than Larian thinks he is. I feel like, given more time, a few more passes and adjustments to the script, he could've been the morally gray and complicated character they wanted him to be. As it stands, he's kind of too obviously untrustworthy and alien and dismissive of humanity to be that.

All in all, I feel like with the way most the rewrites and differences between EA and full release played out, they either should've stuck to their guns and committed to the original drafts or they should've taken more time to iron out the kinks on the current script, because the seams and holes are unfortunately very easy to see