I would not hesitate to recommend Irwin's Hackett edition to anyone who wants to undertake the real work of understanding Aristotle's "Nicomachean Ethics."
The translation & the interpretation underlying it are not perfect. Other translations may in some (even many) cases be based on interpretations I would prefer. So why is Irwin better? Because his is the only version that lets the reader see the nuts and bolts--that is, just how trickily ambiguous Aristotle's text so often is, and just what the translator has done to interpret it and make sense of it. Only with this extra apparatus can a Greekless reader have some confidence in forming his or her own understanding. And even most of us who know Greek are dependent on commentaries and interpretations like Irwin's to force ourselves to confront real issues and possibilities of meaning that we might clumsily miss as we read the Greek.
Since the strength of Irwin's translation is its clearly labelled interpretative moves, I think it is worth considering looking for the out-of-print FIRST edition (ISBN 0915145669). In the first edition, Irwin intrudes his own section headings at the rate of at least ten per Bekker page. These help you know exactly how Irwin is taking the argument (and again, even if you disagree, the value of a translation lies in offering an interpretation that makes some sense). For example, at 1143b6 and following, Irwin's headings say of understanding "It seems to grow naturally..." and then later "...But in fact it requires experience." NO ONE reading the Greek out of context could possibly come up with this contrast, which basically assumes that Aristotle's Greek is misleadingly written (really straining the idea of a result clause, in this instance) in order to make Aristotle make more consistent sense.
Irwin's notes are great. He offers TONS of cross references. It reminds me of a really good study Bible, with zillions of references to other passages packed in along the margins. (In Irwin, these notes are in the back.) Aristotle is a systematic thinker, even if he looks at things from different angles at different times. The kind of comparative reading encouraged by these references is the only way to understand Aristotle.
In short, this is a great edition that lets an English-language reader get into the "laboratory" of interpreting Aristotle. It's not polished, but neither is Aristotle. If you're sentenced to a lengthy jail term, you could take this volume, read and reread it with all Irwin's glossary-essays and cross-refs., and really start to understand how Aristotle thinks. If you were smart, you would end up disagreeing with some of Irwin's translations and interpretations. But it's a tremendous testimony to his interpretative labor that you could disagree in this way. (But if it's a general handle on Aristotle, as opposed to the Ethics, you want, you should really start with Irwin and Fine's Hackett "Selections"--NOT their "Introductory Readings" which deprives you of the glossary-and-notes apparatus really needed to get it.)