Let me preface my own review by offering some insight into the others: most of the poor reviews this book has received have nothing to do with the book's contents; rather, they harp on the formatting and shaping of the text. Focusing on the format of the book and the fact that yes, it is available for free online, shouldn't factor much in a book review, I think, but to this point, it has.
I can see why the publishers formatted it the way they did: to generate recurring sales in that May and June period when most graduations take place, and to make it a pocket-sized, easily consumable text. From a marketing/publishing standpoint this makes perfect sense, and the reviewers hung up on these details seem to be missing the point of the book.
This is why I believe this book deserves 5 stars: any David Foster Wallace follower would be eager, no matter where else the text exists (for free or otherwise), to add to their DFW collection a volume that is so unlike any other he produced. Where his short stories, nonfiction and novels are forever-winding and humanly complex, "This is Water" is a simple masterwork, no less human (and possibly even more so, with its parable-rhetoric) but much less intricate, at least on the most obvious levels. This alone makes the book a welcome addition to any personal library, DFW-focused or not.
The speech itself is warm without being sentimental; it's grounded in reality the way few commencement speeches are, yet it achieves a feeling of inspiration that seems to be, at first thought, highly unlikely, considering the general topic of the speech: surviving the banality of everyday life as a functioning adult.
For those not familiar with Wallace, "This is Water" provides a thoughtful analysis of the realities of adulthood. But for those who have a past with Wallace, the book is a strangely haunting reminder of the principles that drove his writing.
"This is Water" may find itself eventually fallen into that clichéd group of texts given as presents to new grads, though the advice and insight Wallace imparts would be of interest to readers at any stage of life. And as any Wallace fan knows, clichés are there for a reason: they may be molded and generic-sounding, but only because they apply to daily life so universally, not because they are illegitimate and superficial.
It's the same with this book: it may be formatted, shaped and edited into something clichéd and bordering novelty, but the message is so profoundly sweeping and genuine that you would be doing yourself a favor to overlook its commerciality.