After finishing my first campaign and going over to my second playthrough I must say that I pretty much feel the same. It's really demotivating to play through act 1 again and seeing all these plot beats with the knowledge that really none of it has any consequence in the end. You can't really resist the Guardian. You can't really make a deal with Raphael. You can't really find a cure for your tadpole. There's no point in not using all the powers it gives you. There's also the fact going evil feels so hollow now knowing that every evil choice I'm making is basically just going to result in less content for me in act 2 and 3. The illusion is completely gone because the choices that initially seemed meaningful and interesting simply don't really matter.
The illusion of choice is the perfect way to describe this game.
I have to say, for how much we were hearing "reactivity!!!!" over and over again, it's a bit shocking just how limited the ending is. We even have people coping with datamined files that mention cut content that had another possible ending, and they're positive that it's going to come back. Like, that's great for people that might play the game more than once after a year or so, but for the majority of players that play a game a single time at release, they're sort of screwed.
Yes, it's the huge chasm/disconnect between how the game is being advertised and promoted (by Larian, by reviewers, and by fans) as the "new standard" for cRPGs on choices and consequences and reactivity, and the reality of those things in the game, that bothers me so much. If people weren't trying to make these grandiose claims about the game, then I could just accept the game for what it is, which is that it is a good game overall but not particularly better than other good cRPGs. But when people try to make claims about it being the "new standard" in the face of what are indisputable shortcomings, for me that hurts my appreciation of the game rather than helps it.
