Of course, having been an English major (among others) in college, I'd encountered Yeats in various settings, but as the years have gone on I've come to realize how “not deep” (to avoid calling it “shallow”) one's exposure to the literature is even in top-notch Liberal Arts programs, and I've attempted to plug in missing bits as they've come up.
The current volume is W. B. Yeats: Selected Poems (even though my copy has “William Butler Yeats” spelled out on its dust jacket and spine), although from reading other reviewers' snipes, I guess it should more accurately be called “the early poems” as it seems that his later, better, more popular material did not make it into this volume, for whatever reason (much to some critics' irritation).
Perhaps this is why I didn't really get particularly enthusiastic for anything in here … it's quite a mish-mash of styles and voices, subjects and formats, ranging from 6-line barbs at a bird for reminding him of some lost love, to 12-page rambling retellings of Irish cultural myths, to broadsides against deadbeat would-be sponsors. It does, however, include one of his more famous poems, September 1913, which is of his political oeuvre.
Yeats was also deeply involved with Theosophy and the Golden Dawn, but (as conversant as I am on those subjects) that influence does not seem to come through much in this collection, as the places where he does get “mystical” are primarily in “Celtic myth” poems, almost all of which here are pulled back to some sort of Christian framing by the end of the piece, or have it end up being more about lost love.
That's another point here … the first part of the book all seems to be about loss and sorrow, scarcely a poem goes without some mention of heavy sighs over things that might have been … I don't know if that's from “callow youth” or the stylistic form he was emulating at the time.
Of course, my tastes in these things are fairly constrained to a few general streams, and I might just being cranky here, but this particular collection didn't do much for me, but you might find it far more interesting. He kept almost getting me into a particular piece, only to run off into something that was not to my liking … quite frustrating.
Anyway, this particular W. B. Yeats: Selected Poems (by Gramercy Books) seems to be out in a variety of versions (and covers), but can be had for as little as a penny (in a “like new” copy of the hardcover), so it you are interested in catching up on Yeats' early work, it won't set you back much.