Some of the books are small stories that take part throughout the ages and have different characters. In the series they decided to have the same protagonists, so they went through insanely convoluted plot devices to achieve that and to move them around the place and have them being related.

But my real issue is that they really changed not only Hari Seldon's and "Demerzel"'s characters but what the series is about. They are kinda making it a religion and then say "oh it isnt a religion thing, it is just a tool, oh nvm, it is a religion, ha just kidding, not a religion or maybe it is". The foundation series is pretty atheistic in nature. And while religion is used(as a tool against the outsiders), the tv series makes Seldon a televangelist.

The tv series is full of deus ex machina and not even good deus ex machina. Maybe they felt the initial stories would appear somewhat simplistic and tried to modernize them and make them "edgy". Generally, 90% of the plot isnt from the books.

"Demerzel" is a couple characters combined from the books but ultimately she is the most important character of the show(well i assume so, because she isnt a 1:1 character from the books). And she cannot be religious.

Most of these issues could be solved by simply renaming the series and some story editing to make it tighter and less convoluted. You dont need to have the same characters be everywhere, at every period and be related to each other, it is silly and cringe, just like Rey ~~Palpatine~~ Skywalker.

I will still watch future seasons and the show has many stories and scenes that are great(most of the Empire stuff, which are original). But even without knowledge of the books, i feel those artificial story arcs that try to connect characters are bad.

TLDR : If the books are Star Trek TNG, the series is Star Trek Discovery