This translation of the Quran has one of the best commentaries I have read. Many verses in this translation are explained in the footnotes. References are given for most of the footnotes/explanation which helps the reader realize that the explanation given is not the translator's own opinion.
A footnote/sidenote is added whenever the translator thinks that a word in Arabic needs further clarification or can have more than one meaning.
Many times in the translation, the occasion when a given verse was revealed is also given which helps the reader learn Quran better. An attempt has been made to describe a verse of the Quran using another verse of the quran based on the saying of Imam Ali(a.s.) that one part of the Qur'an verifies another part. The other source of explanation of the verses are sayings of Holy Prophet(peace be upon him) and the sayings of the Imams of his family(peace be upon them).
Sources from the Ahl-Sunnat school of thought are also adequately mentioned, although that is done primarily to strengthen a particular point that is mentioned in the translator's footnotes.
Overall, this is a great work and should be read by anyone who is interested in learning about Islam, Quran and Islamic History.
However, there are also some defects in this translation/edition. The paper used is very thin but this was probably necessary because the explanations are in detail and exist for many verses. There are a few verses for which there are some typographical errors, e.g. missing dots. Some verses have incomplete translation, for example, the translation of 8:48 is missing the following portion of the ayat, "Inni Akhaf Allah" which should translate as "Surely I fear Allah". Someone with rudimentary knowledge of Arabic should be able to spot these mistakes.