This is really more of a dress, or a very over sized shirt. For me is falls just above my knees (I am 5'8) and I went with the medium. I will typically size up in shirts because I like the over sized look but I am so glad I went with the medium- I can't imagine how big the large would have been on. Its going to be very cute with a pair of leggings or ripped up tights.
Also the open back is very alluring, I've gotten many comments on it already. Nikita is one of my favorite brands and they have yet to disappoint!