In the beginning of Sha'ar Daled of Nefesh HaChaim, Rav Chaim of Volozhin criticises those people who do not engage in classical learning, but instead spend time studying "Sifrei Yirah U'Mussar." Which seforim might he be referring to? Were there particularly popular Seforim being learned during this time?
If you continue to read to the end of that first chapter in Sha'ar 4, the intention of Reb Chaim is understood.
He refers to what he calls "Gufei HaTorah" (the bodies of the Torah) which he defines as the written Torah, the primary body upon which all else is built, and oral Torah, meaning Mishnah and final halacha, which is the second body.
He contrasts this category with those books which were written to help the individual refine themselves and their personal character traits, what he calls earlier the Sifrei Yirah and the Sifrei Musar.
At the time of Rabbi Chaim, a few of the popular books in these later categories were Mesillat Yasharim by Ramchal, Reshit Chochmah by Rabbi Eliyahu De Vidas, Chovot HaLevavot by Rabbi Bachya bar Yosef ibn Pakuda and Sha'arei Teshuva by Rabbi Yonah bar Avraham from Gerona.
What Rabbi Chaim was emphasizing is not that people were not engaged in classical learning, but that their emphasis had been reversed. That which was held classically to be ones primary area of emphasis in study was the written Torah and halacha l'maaseh. Character development is secondary to knowing the written Torah and what to do in actuality in regard to mitzvah fulfillment.