(I expect there is a DOT Prophetic Books [Isaiah, Jeremiah, etc.] planned for the near future, though I couldn't find any mention of one on the IVP website.)
While this makes them expensive over all, the quality and quantity of scholarship they make available makes it worthy investment. I have bought this DOT Pentateuch and the DOT Historical Books in the last couple of years and hope to get them all eventually.
Even though I emphasise that this is a series of dictionaries, each individual volume still represents a complete and comprehensive unit. A vast array of topics are covered, usually in fairly significant (but digestible) detail. One of the first, for instance, is `Agriculture' (p21) which spans the next five pages. This article is clearly subdivided into four sections (`Crops' is further subdivided): Geography, Livestock, Crops and Theology (which serves as a conclusion). Here the writer, D. W. Baker, emphasises that agriculture and agricultural imagery are used in the Pentateuch to illustrate how strongly the Israelites linked the creation and sustaining of the natural world directly to Yahweh. He ends noting that the Song of Moses (especially Deut. 32:13-14) focuses on the `literal fruits of faithfulness'.
(Compare the `Agriculture and Animal Husbandry' article in my DOT Historical Books review on Amazon.)
The uniformly clear and comfortable reading format and overall aesthetic layout also make them a single reference work. There is a continuity of articles too - at least in the absence of repetition. For instance, of the two volumes I own, the entry for `Angel of the Lord' (directing you to `Theophany', from the Greek for `god' and `to appear') only appears in the Pentateuch volume. It's easy to see this as an error of omission if you only own the Historical Books volume, but I imagine each volume would be larger and even more expensive if articles were duplicated. (Perhaps the omission of `Spirit' or `Holy Spirit', etc. from both volumes would be covered in the Wisdom or (potential) Prophetic Books volumes?)
The only real criticism I have is that digital media would be more convenient in many cases. While I have always preferred books as opposed to disks (and vinyl as opposed to CDs), still the digital media so much cheaper and easier to use. I have owned Essential IVP Reference Collection CD-ROM (mine is version 2) for years but could never have afforded all the superb New Testament reference books which it contains. I hope that IVP will have an Essential Collection for the Old Testament too, one day.
In the mean time, this is a hugely expensive series but worth every penny, which I think of as an investment, not an expense. I suppose you could say, `you get what you pay for' and paying for this title - or series - gets you supreme quality: highly recommended.
EDIT: I note that the Logos Bible Software website now lists the Pentateuch and Historical Books dictionaries as 'under developement'. So someone is digitising them - or two of them, at least. ('Pre-Publication' price is lower, if you're quick...)