Rav Israel Salanter began the Musar Movement with the awareness that to be a mensch [good character] is a main thing-- even though this might not be clear from a straight reading of the Oral and Written Law. to be aware of the importance of 'midot tovot' good character really takes faith in the Rishonim. But this message has been lost in time. Even in the great Litvak yeshivot where Musar is learned, this emphasis on good character traits has been lost while religious fanaticism has taken its place [or all sorts of other weird ideas]. What ever happened to straight Torah? The best idea therefore is to renew the Musar Movement--but this time not to mix it with foreign ideas. Just straight Musar of the Rishonim [and the books of the disciples of Rav Israel Salanter that go along with that approach.] 

And remember what the Rif and Rosh wrote about "Outside books" ספרים חיצונים [that one loses his portion in the next world by reading]-books that explain the Torah in ways other than the Midrash of the sages. Most religious books come under this category. 

Why Rishonim are important is that in philosophy and logic the Middle Ages excelled in rigorous logic even though the axioms were often faulty. After the Middle Ages even the best of  authors were often guilty of circular logic..