It is argued that in our current digital era, MALL (mobile-assisted language learning) is an indispensable mode either for independent self-learning or for integrating with the school curriculum. The present study explores the possibility of using gamification as a home assignment in English as a foreign language course for students of non-English majors at a university in Vietnam. Data was collected and analyzed using 69 questionnaire responses and 41 essays written by students in a class of General English. The questionnaire and essay topic prompt required students to provide an evaluation of their personal experience learning English with Duolingo outside the classroom, as part of the compulsory home assignments during a 15-week semester. The questionnaire items were in Vietnamese and the essays were either in Vietnamese or English for students’ convenience. The results showed detailed benefits and problems of learning English with Duolingo as perceived by the students. The key benefits include the fact that Duolingo is a valuable resource: rich and free; the limitation is mainly learners’ lack of experience with the application. It is suggested that with teachers’ guidance, Duolingo could be used as an effective and motivating tool for independent learning.