Prelude to Foundation & Forward the Foundation

Now, after having read the Foundation prequels as well, I would say that one might be better off just going through the original trilogy and leaving it there. You won't get a conclusion to Seldon plan (though how much do you get even with the sequels?) but you will keep the series separated from the 0th Law of Robotics. The trilogy will stay as a centuries spanning galactic struggle just among humans. These two prequels do at least bring back the Encyclopedia Galactica epigraphs I missed in the sequels.

Risen 2 - Dark Waters

Risen 2 - Dark Waters takes the series into a pirate themed direction. The still-nameless hero, currently a soldier of the Inquisition, goes undercover to put an end to another Titan threat. Shields, plate armor, and arcane magic are gone and instead you get cutlasses, muskets, and rum. There is also voodoo magic if you decide to side with native tribes.

The Dark Forest

The Dark Forest (黑暗森林 / Hēi'àn sēnlín) is the second novel in Liu Cixin's Remembrance of Earth's Past trilogy. The Three-Body Problem was a good read but I think this one had even more deliberation put into it, making it feel like an important work of science fiction, mainly because of it coining cosmic sociology. The sole thing I didn't like in the novel was the viewpoint of a Chinese navy officer Zhang Beihai whom I thought boring and the little payoff at the end not worth it for the time spent on following him.

The Way of Kings

The Way of Kings begins Brandon Sanderson's fantasy epic, The Stormlight Archive, which is currently at four published novels out of ten planned. The series has garnered a lot of praise but I personally went in with low expectations, kind of anticipating typical Sanderson cast of characters, same old traits shuffled around a bit.