There are many different Bible commentaries today, some are good, some are not so good. Some are written by trustworthy men of doctrinal integrity, some are written by men which lean more toward a liberal or critical approach. Some fall in between. As always, this is a matter in which we must exercise great discernment. We would not want to read a commentary written by an unreferenced source. Our selection should be based on some reliable knowledge or hearty recommendation of the author by men whom we know and trust. At the same time, it is so important to remember that no commentary will see eye to eye theologically with everything in which we believe. We will at times find ourselves disagreeing with the writer's interpretation of this or that passage or of other important issues. This should not at all though discourage us from consulting them. It is helpful when reading commentaries to always remember to, "chew up the meat and spit out the bones" or "take the good and leave the bad". Who is to say that we are always right anyway?
More so, commentaries are not all the same, different types of commentaries serve different purposes. Many are good in their respective areas of attention. I have chosen to divide them up into three groups of my choice to see the differences and purposes of use more clearly: Devotional, General, and Greek Exegetical:
Devotional Commentaries often give a general overview of the entire Bible, or of specific books, while focusing primarily on main themes and practical application for the Christian life. As such, they are not going to be as focused on detail as others may, however they are still very useful, valuable, and are not to be underestimated. These commentaries can be very good for devotional reading and study.
General Commentaries are commentaries of individual books of the Bible. These pay much more attention to detail in the realm of theology, history, culture, background, contemporary issues, application, and occasionally consider the original wording. Though at times they may be semi-technical, they should still be accessible to any serious minded Christian who is willing to dig deep into God's Word; however, a working knowledge of Greek may at times help. These commentaries can also can be of great use to the pastor, preacher, missionary, and theologian.
Greek Exegetical Commentaries, like the previous group, also focus on history, culture and background. Some writers will give less attention to theological issues than others, as their main objective is to expound the meaning of the Greek text and not write a theology book. The primary difference between this group and the General Commentaries is that these are much more technical, being based on the Greek New Testament text, as opposed to the English New Testament, and as such, they are written for those with a working knowledge of NTG. These focus on the original language for the purpose of exegesis, interpretation, and to see nuances and meanings of language which are not seen clearly in English. Because of this, they will usually demand a working knowledge and understanding of NTG in order to be able to profit from them without getting lost. Some of them may still be used without a knowledge of Greek, however their use will be rather limited.
Since we are talking about NTG, I want to recommend some of the most scholarly and trustworthy commentaries based on the text of the GNT. I will be updating the list from time to time so check back periodically.
The link below contains the two other categories of commentaries as well. The Greek commentaries are listed third:
Greek Exegetical Commentaries