In terms of its themes of Love, Death, Eternity, and Transience, Keats's poem is very accessible. Like, we know that these themes are pretty heavy and all, but we're also pretty sure that just about everyone has spent some time – probably late at night – thinking about these sorts of things. Of course, when most of us were thinking about them, we probably weren't thinking of words like "Eremite," "ablution," or "swoon." So, yes, there's some unfamiliar vocabulary in the poem that can be a little bit tricky – though dictionaries and our "Detailed Summary" of the poem here on Shmoop should help clear these problems up.
Another thing that might be a little tricky in Keats's poem is the syntax – a fancy word for the way the words are put together to form sentences. Wait – did we say "sentences"? Our bad: we meant "sentence" – did you notice that Keats's poem is actually just one long sentence? And let's face it: if you're going to stretch one sentence out over fourteen lines, chances are there are going to be some twists and turns along the way – like when Keats makes us wait until line 5 to hear what the star was "watching" back in line 3. Once again, our "Summary" should help you make sense of these problems. Really though, the challenges of Keats's poem are small potatoes compared to what makes it accessible – its universal themes that have something to say to everyone.