I have read both the New King James version and the English Standard version. I have noticed very trivial differences between the two. What, if any, are the major differences between the NKJV and the ESV?
The New King James version is meant to be an update (circa 1975) of the vocabulary and grammar of the King James Version, while preserving the classic style and literary beauty of the original 1611 KJV version. 130 translators used the original King James version as well as Greek, Aramaic, and Hebrew texts including the Dead Sea Scrolls. The translators have sought to follow the principles of translation used in the original King James Version, which the NKJV revisers call "complete equivalence" in contrast to "dynamic equivalence" used by many other modern translations. The task of updating the English of the KJV involved significant changes in word order, grammar, vocabulary, and spelling. One of the most significant features of the NKJV was its abandonment of the historic second person pronouns “thou”, "thee", “ye”, “thy”, and “thine”. Verb forms were also modernized in the NKJV (for example, "speaks" rather than "speaketh").
The English Standard Version (ESV) of 2001 is a revision of the of the 1971 Revised Standard Version, which traces it's origins to William Tyndale's New Testament translation of 1525 (the first English translation of a Bible from the original Greek and Hebrew manuscripts, which was also a significant influence on the original KJV). Work on the ESV began over the perceived looseness of style and content of recently published English Bible translations. Many alterations designed to correct or improve the text were made to satisfy the objections of conservative Protestants who had considered the RSV to be theologically liberal, for example, changing the translation of the Hebrew almah from "young woman" (used in the RSV) to "virgin" (in the ESV) in Isaiah 7:14. The language was modernized to remove "thou" and "thee" and replace obsolete words (e.g., "jug" for "cruse").
Relative Differences: the biggest practical difference that I can see is that the ESV is newer. The RSV, upon which the ESV is based, was primarily a project to update the Bible to the English language of the current time (mid-20th century) as an improvement over the old KJV. By the time the ESV was published the New King James Version -- which also had as its goal to modernize the language -- had been published twenty years earlier. It seems to me (a Catholic who primarily uses the Challoner revision to the Douay-Rheims and the Latin Vulgate) that the both the ESV and NKJV are projects which in their history are based on the same work (Tyndale's Bible) with the same general goals (modernized language) and which have both achieved this goal with negligible qualitative differences.
One of the main differences between the ESV and NKJV is the underlying Greek texts. The ESV uses whas has been called the Critical Text whereas the NKJV uses what has been called the Received Text. The differences between these underlying greek texts is not insignificant. A discussion of the differences between them is likely not appropriate for this venue. My personal preference is for the Majority Text which is very similar to the Received Text in almost every way as the vast majority of greek manuscripts fall into this family.
The essential difference is that the NKJV is a revision of the KJV and so shares the same textual basis as the KJV, that is, the Received Text, whereas the ESV is a revision of the RSV and shares its same textual basis, that is, the Critical Text. The Received Text is the text which most consistently corresponds to the fulfillment of God's promise to preserve his Word for his church. The Critical Text involves at least some setting aside of that promise, if not a downright ignoring of it. In other words, the theology behind the choice between the two texts is vastly different. This important difference is unfortunately too often overlooked. The ESV is in no sense a continuation of the same approach to Scripture as was held by the translators of the KJV. The ESV is the result of the application of quite a different approach. But most people are quite unaware of that fact, and certainly the publishers of the ESV make no effort to inform them of it, probably because they themselves regard it as an unimportant fact and do not wish their readers to hold any other view.
I am no scholar but I have found the NKJV to be a more literal reading, e.g. Romans 12:16 in NKJV says, 'Be of the same mind toward one another...' and the ESV says, 'Live in harmony with one another...'. I easily understand both texts but wouldn't you agree that the NKJV is a more literal, and therefore more accurate, reading of God's Word?