Larian says that the intention behind the changes they did to the rules is to make the game more FUN, with some homebrew rules. I say it is not funny at all so far.
D&D 5 is successful because of a loooong experience in what is balanced or not in the game (and it worked quite well in BG1 & 2 when they respected former D&D editions btw). And, we, - d&d 5 players - are the experts of what is balanced and what is not.
We have said numerous times that the way it is done is not balanced. When it is not balanced, well, it is not FUN. This is so simple actually, isn't it ?
We are not naive and we know that 100% of the rules/spells cannot be implemented. But we also know that it would be possible for 95% of them. And it is far from being the case at this stage : it even does not respect very core and fundamental rules of D&D5. For more fun ? Well, too bad. It is not.
You could have it all, Larian. Please be as close as you can to D&D core rules, you can do far better, and we already know it will be extremely funny for D&D players, and still quite funny for non D&D players. Do this Larian, and you know we will follow you in any sequel of BG you'll make.