...apart from them falling apart (pun intended) in Act 2, that is.

It's the inability to stick to the theme it's trying to embody, and even downright contradicting it.

At least in EA and from what can be seen with the companions in the main game, it can be argued that the throughline the game was probably intended or at least attempted to go with were it not watered down in the end is the loss of self and the fear of that happening. The idea that you are a host to something that will, if untreated, erase you as a person and remove you from existence while your body continues on, now hosting a cosmic aberration. At least that is what the Early Access Daisy interactions and the comments by the companions on their illithid powers, together with the implications that using tadpoles "takes something from you that you'll never get back" have been implying.

As for the companions, we have:

- Lae'zel whose entire worldview crumbles as she discovers the truth about her people (combined with the tadpole),
- Shadowheart whose past has been forcefully erased and whose whole persona is an implanted lie (combined with the tadpole),
- Gale whose pursuit of Mystra and magical omnipotence turned him into a walking disaster waiting to happen (combined with the tadpole),
- Wyll who took a pact which turned him into an exile from his own city and family (honestly, his plot was framed a lot better in the EA, what with him actually having a lot more meaningful conflict with Mizora seemingly, and yes, combined with the tadpole),
- Karlach, turned into a living weapon and forced to fight for her archdevil mistress (combined with the tadpole),
- Astarion, effectively enslaved for two centuries and his live self all but dead (combined with the tadpole),
- Minthara, whose memories were deliberately suppressed so that she follows Orin's and the Absolute's commands without question (combined with the tadpole),
- ...and Jaheira, Halsin, and Minsc, mostly for fanservice. Ahem.

The problem arises with the whole "combined with the tadpole" aspect of it. Instead of it being a threat and a risk to use and something to remove at all costs, it's ultimately presented as... a source of cool superpowers. Rather than have the characters either hang on to what they know they are and maintain every last aspect of their selves - or give up and allow their being to be overwritten by the combination of a tadpole and Netherese magic, they instead have a single rough night and any threat from the tadpole is otherwise neglected. And then comes the Emperor, who basically represents the contradiction in the flesh:

- No, apparently becoming an illithid isn't an irreversible erasure of a person who was the host for the tadpole, despite the game itself mentioning that very fact at several points (Lae'zel and Withers come to mind right away). You get even more cool superpowers!

- No, you don't cease to exist as soon as you transform, if you have a "strong personality(tm)", you get to keep your memories and your self, now with a "superior(tm)" physical form to boot!

- No, why would you shun becoming a mind flayer, never mind the fact that you will have to conceal yourself if you hope to interact with the surface society in any way and sustain yourself on brains (obviously ethically harvested from "criminals", forget about what makes the criminal in the first place) while no longer having neither your mind (no matter what the Emperor says) nor your body!

- Apparently tadpoled people can just change at the drop of the hat by really wanting to, and even non-tadpoled ones (Orpheus), even though the process was supposedly suppressed! Hell, the plot point about "only a mind flayer can counter the Netherbrain" would have worked so much better if the game actually presented becoming a mind flayer as a genuine horrible outcome and clearly displayed your character no longer being themselves when they do transform, being an actual sacrifice for the greater good that you either make, or let the Emperor manipulate you to the bitter end. Or make unwillingly transforming an actual risk and an actual threat when facing the Netherbrain, having the "strong personality(tm)" be a way to offset changing in the first place, either through power or through all the bonds you are allegedly building with your companions throughout the game. Have Daisy back and make his/her pull (and through it, the Netherbrain's) ever stronger the more you succumbed to the tadpole, offsetting the powers you got with having to reap the consequences of abusing them... but also giving you a way to actually overpower the leash if you well and truly commited to being an illithid hybrid or something.

This risks turning into a rant more and more with each sentence, so I'll stop here, but I am curious as to what others think regarding this point and what their ideas for fixing the plot might be.