Despite an increased awareness of language learner performance in task-based instruction, little is known about how learners perceive and respond to different task factors. This study investigates the effects of task complexity and modality on (a) learners' perception of task difficulty, skill, and its balance, and on (b) learners' task experience. It adopts Csikszentmihalyi's (1975) construct of flow, characterized by interest, attention, and control. It further examines how difficulty-skill balance predicts flow experience. In a repeated measures design, 141 learners of English as a foreign language (EFL) performed 4 argumentative tasks that differed in task complexity (+/-elements) and modality (speaking vs. writing), and completed a questionnaire asking about their perception of task difficulty, skills, and task experience. A repeated measures multivariate analysis of variance showed that, although both task complexity and modality affected learner perception of task difficulty, only modality influenced perceived skill and flow; writing provided more favorable task experiences regarding the difficulty-skill balance and flow. Furthermore, difficulty-skill balance significantly predicted flow experience, but the condition seems insufficient for affecting flow.