When it comes to Plotinus, you should look for something by Arthur Hillary Armstrong if you want to be well-oriented. Armstrong explains Plotinus in several places at various lengths, and translates the acclaimed Loeb edition—the introduction to which may be too brief, but is still cogent. After Armstrong I think Bréhier is the best. His 1922 lectures lead you into Plotinus in a very engaging way. He is very learned, Bréhier, wise in his approach and not at all like everybody else who explains Plotinus: he comes at everything from one single, fundamental tension. I think Blumenthal is a radish. Learning is now conducted without humanity or elegance, by a kind of madness of method, largely, part of our civilization’s longing to hear the toilet in which it resides flush.
Be that as it may, introductions are important when it comes to Plotinus, because he was so different, so great, and so hard to just pick up and figure out. Plotinus, let me say again, was very great, a serious man. He is worth knowing by anybody interested in that which is worthwhile. What he is not, however, is readily accessible. For me, you have to know his system first, and then he is negotiable. No doubt there are persons who can just pick up a treatise by Plotinus and figure it out, for the rest of us there are necessary introductions.