Ok so this is gonna be a controversial one but here we go:
Let's face it: The AI trailer looked much cooler than the actual game we have now. There are MANY things that should be brought back from the AI trailer.
Neural Network: Let's start with the most obvious and important one. TinyBuild was objectively in the wrong when they removed any mention of a neural network AI days before release. While I think learning from the community would be cool at first, it wouldn't work in the long run since the game would just become impossible in smaller areas like Otto's house. You could bring back the community-learning neural network in future updates where bigger locations are introduced, but if we're talking about now, I think a neural network that learns exclusively from the individual player would be quite cool, as it would have the daily routines, pickup-able items and status effects advertised in the trailer.
Aesthetics: The new artstyle fits the game much better but one thing I do think was universally agreed to be better was the pre-beta lighting and foliage. The more toned down colours of the alphas and the AI / E3 trailer, and the foliage there looked 10x better.
Quentin: The player movement seen in the alphas were much nicer and smoother than the more floaty and robotic movement we have in the final game, specifically when jumping and mantling.
Locations: The mall would be a 10/10 location so bring that back, as well as the 8 locations that were said to be there in "Alpha 2". Now for Gray Manor, I would not mind that replacing The Museum (or maybe even as a new location) at all as the more claustrophobic environment would feel much nicer and more suspenseful as a stealth game instead of the completely open Museum where, a lot of the time, you can easily see threats coming towards you.
Well, that's it for this post! If you agree and want Eerie Guest to see this give it a bagger thumbs up! And if you think there's more suggestions feel free to comment them!