It is a perennial amazement to me that many folks actually believe that the NIV is a "better" translation than some of the older translations, such as the KJV.
As a translation, it really is not better. It frequently attempts to convey the sense (as determined by the translation committee) at the expense of the literal expression. When it does this, it mixes the roles of translators and commentators.
Certainly, we must agree that sometimes judgment as to the sense is required when making translation, but the NIV is quite free in many places. This fact was immediately demonstrated by advocates of the traditional translations, but it seems that the word is not out there.
Likewise, we must agree that one could do far worse than the NIV. There are translations that employ deliberation mistranslation (such as the New World translation) and gender confusion (such as some of the feminist translations). There are also translations that are little more than paraphrases of an earlier English translation.
One thing that complicates the analysis is that the NIV relies on the so-called "critical text," rather than the more traditional "majority," "Byzantine," or "textus receptus" texts. In consequence of reliance on the "critical text," in some places the NIV omits material that ought to be included, though some of the omission is at least partially made up through the use of footnotes.
Another thing that complicates the analysis is that the KJV uses some terms that have become non-standard or archaic, or for which the meaning has changed over the years since the KJV was published. Typical anecdotes along this line recount the congregational bafflement over "Suffer the little children" in the KJV text. "Why would God want little children to suffer?" was the punchline question of the humorous account.
Thus, because of the challenges associated with building a varied vocabulary and understanding the beautiful intricacies of the language, some people have attempted to find versions that lack the flower language and challenging vocabulary of the KJV.
Neither of those issues, the translation source document or the wording style, is really a translation issue per se, though both issues are well connected with the translation procedure. The former is a pre-translation consideration, and the latter is a matter of expression - which is well within the freedom of the translators.
This author is not one to call it the New Idiot's Version, but the NIV is simply not that great. If one must have less flowery and precise words, more modern vocabulary, and translation based on the questionable critical texts, then go with the ESV or the NASB, not the NIV.
Please do not get this author started on the TNIV.