For more information on the Logos Bible Software’s digital edition of Moulton, Howard & Turner's Grammar of New Testament Greek, go here and here. For a discussion of the significance of this publication in the history of New Testament research, go here. Below the fold, Part 1 of Michael Aubrey’s review.
This is going to be a rather pragmatic review. I will focus on content and, as one must with a digital edition of a resource, capability. Finally, I will discuss what for many people, including myself, is the most important question: price.
For the sake of brevity, when I refer to the entire four volume set, it will be abbreviated MHT. When I refer to a particular volume, it will be MHT1, 2, 3, or 4.
Some scholars consider much of what Moulton wrote to be outdated now that what has become known as "Verbal Aspect Theory" has gained so much strength in recent years. But is this the case? I think not.
As I type this review, I have MHT1 pulled up in Logos. To my right is a copy of Stanley E. Porter's Verbal Aspect in the Greek of the New Testament with Reference to Tense and Mood. Throughout much of Porter's work, we find a rather critical view of "Aktionsart Theory," which has been considered the traditional model. But the true problem is less one of "theories" and more one of terminology.
Aspectual studies originated with the examination of the Slavonic languages, such as Russian, and then applied to the study of Indo-European. Much of this work was done in German. The tendency has been to understand the German term Aktionsart as a synonym of Aspect. As linguistic studies have advanced, a distinction was made: Aktionsart is presently used in linguistic circles as a subset of Aspect.
Thus, in David Crystal's very handy Dictionary of Linguistics and Phonetics, aktionsart is defined as "lexical aspect" rather than grammatical/morphological aspect. The definition that we often hear in NT studies, that aspect is the subjective perspective of action while aktionsart is the objective description of an action is one I have never heard outside of Biblical studies. Neither had my advisor in my linguistic field methods class who wrote his dissertation on Aspect.
These facts are crucial to our understanding of the grammars written in the last century, particularly those that had such a great impact such as those Moulton and Robertson (go here for an introduction). The fact is that neither Moulton nor Robertson necessarily intend to describe objective action by the term Aktionsart because it was the only term available to them. Whether this is true of Turner's discussion in MHT3 is less than clear to me.
With this is mind, Moulton's discussion in chapter six of MHT1 begins to appear quite modern, even more so when we realize that 1) Aktionsart means Aspect, 2) Punctiliar means Perfective, 3) Durative means Imperfective and so on. This is especially clear when we note that Moulton regularly uses the present aspectual terminology in reference to those verbs which are derived from the affixation of a preposition. 
The choice of the preposition which is to produce this perfective action depends upon conditions which vary with the meaning of the verbal root. Most of them are capable of “perfectivising” an imperfective verb, when the original adverb’s local sense has been sufficiently obscured (MHT1, 111).
And then when we combine Moulton's understanding of lexical aspect with his understanding of morphological aspect, the result, rather than being archaic and outdated, actually begins to look like a blend of Porter's work on Verbal Aspect as a morphological category and Moisés Silva's work on Aspect as a lexical category (see, for example, chapter 1 of his Interpreting Galatians: Explorations in Exegetical Methods).
All of this to say that the greatest gaps between modern grammatical and linguistic study has more to do with terminology than content and that MHT continues to be a valuable and helpful work. Dare I say, it is a necessary work for advanced students.
 The reason behind this is simple. These are terms that originally were used to describe Russian aspect, where the only aspectual distinction was the derivational application of a preposition (and thus Lexical Aspect, i.e. Aktionsart). For that reason, one could say that Porter is just as wrong in using the terms perfective and imperfect since they historically referred to lexical rather than morphological aspect.