Several schools have implemented "Learning Assistant" (LA) programs, in which upper-class undergraduates serve as teaching assistants in introductory courses. At UNCG, LAs are given an unusual degree of freedom. Working in teams, they serve as the primary instructors for lab sections of the two introductory calculus-based physics courses. They co-design the lab curriculum with the professor of the lecture section, conduct all lab classes, and grade all student work. In order to investigate how students taking the lab reacted to having undergraduates as lab instructors, we gave and analyzed a short anonymous Likert-type survey probing students' opinions at the end of the first course. We found that overall, most students reacted favorably. They found the LAs' content knowledge and pedagogic skills to be adequate, and saw some benefit to having undergraduates rather than faculty to interact with. They also perceived that the responded to questions with guiding questions rather than authoritative answers.