The strength of the NIV is that it reads very smoothly (or at least, the 1984 version did). But IMO this has been achieved by a certain looseness in its accuracy. One of the most annoying things one finds is the absence of certain conjunctions, notably 'for' and 'therefore' (or 'so'). Two examples, out of dozens one can find:
Isaiah 12:3 (NKJV). 'Therefore with joy you will draw water from the wells of salvation.'
Isaiah 12:3 (NIV). 'With joy you will draw water from the wells of salvation.' The ESV is similar, but that is not my concern.
The drawing of the water, is contingent upon knowing God's anger to be turned away and Him as one's salvation. There needs to be a connecting word to make that clear. 'Therefore' is a big 9 letter word; 'so' or even 'and' would do nicely.
Romans 1:18 (NKJV). 'For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men. The ESV is similar.
Romans 1:18 (NIV). 'The wrath of God is being revealed from heaven against all the godlessness and wickedness of people.'
The reason that Paul is not ashamed of the Gospel (v.16) is because it is the power of God to salvation. And that is vital precisely because the wrath of God is currently revealed from heaven. The Greek preposition gar is there for a reason; to connect verse 18 to what has gone before. While I'm on this verse, 'wickedness' is a loose translation of adikia. It is the lack of godliness and the lack of righteousness for which God's wrath is revealed. I recently preached through Romans 1-8 in the NIV (1984), and I was constantly having to point out where prepositions had been left out.
If I had to choose the one most important quality in a Bible translator, it would not be intelligence or scholarship or knowledge of the original languages, vital as all these are. It would be humility. Anyone setting himself to translate the Bible is handling the very word of the living God and he should be aware of that, and do the work, metaphorically at least, on his knees. If ministers and Bible teachers will be judged more severely by God (James 3:1), how much more strictly again will translators of God’s word be judged, seeing that they have the power to lead or mislead tens of thousands of Christians as they do the work well or badly.
Seeing that ‘every word’ of God is pure and therefore important, the Bible translator will seek, in the fear of God, to make as faithful a rendering as he can. Everyone with even a smattering of Greek or Hebrew knows that an exact word-for-word translation is not possible. Sometimes people give examples of an entirely literal translation, and then suggest that since that ‘won’t do,’ the translator is free to muck about with the text until he comes up with something that seems right to him. This is not so. The same people take, perhaps, the K.J.V. translation of 2 Cor. 6:12; “Ye are not straitened in us, but ye are straitened in your own bowels,” and say that it does not make much sense.’ Well, it is hard to understand for many people, but that is not the same as saying that it makes no sense; it made perfect sense in the 17th Century, and still makes sense to those who are prepared to make an effort. However, it is not the texts that are difficult to understand that are the most dangerous. If someone doesn’t understand something he can go to a dictionary or a concordance, or ask his minister. The really dangerous texts are the ones that are in simple, plain English, but are translated badly. People won’t ask about these because they think they understand them. Let's look at 2 Cor 6:12 again.
2 Cor. 6:12 (NKJV). 'You are not restricted by us, but you are restricted by your own affections.'
2 Cor. 6:12 (NIV). 'We are not withholding our affections from you, but you are withholding yours from us.'
The NIV translation is pure paraphrase, and does not convey what the original says. The NKJV tidies up the KJV translation a bit (though 'bowels' is actually what the text says!) but conveys what Paul is saying.