NCIS works well for learners who already understand English comfortably and want more challenging listening practice. Some scenes use denser language, so learners may need to pay close attention to word choice and phrasing. With the dialogue moving at a natural rhythm, viewers should catch most of it, although a few moments may still be challenging. There is enough plot detail to keep learners engaged without making the whole experience confusing. If your English is close to B2/C1, NCIS can be useful for building vocabulary range.
