9.5/10
Just see Jacob Aitken's review above. This was one of the first works of analytic theology, which still was just as much analytic philosophy of religion (cf 'The Logic of God Incarnate', a similarly early book straddling the divide) as the analytic theological work carried on today by Crisp, Hudson, Rea, McCall, Pawl, Plantinga, etc.
Helm proves his points and proves them well; they've stood for 30 years, and will stand for many more. He focuses on divine eternity, its first degree corollaries omniscience, immutability, and aseity, and its second degree corollaries determinism and the possibility of interaction with creation. Chapters 7 and 8 on holy determinism are some of the best in print, and are an excellent complement to 'The Most Real Being'. He closes with a chapter on the possibility of referring to or identifying a timeless eternal being from inside a temporal series, and in this the second edition adds a 60-page appendix refuting some of William Lane Craig's philosophical nuttiness and theological heresy (only some, because it is endless), viz. the idea that God 'was' eternal but is now temporal and sempiternal, the A-series of time, the coherence of middle knowledge in Craig's God, and finally closes with a chapter of analysis of the doctrine of eternal creation.
Contra the 3-star review above, though the author is a Westminster Confession Calvinist, I'm a Thomistic Catholic, and found the book excellent, as will anyone with interest in analytic theology. The only reason you wouldn't is if you hold an irrational, preconceived notion of the absolute necessity and truth of libertarian free will, in which case you can't believe God is eternally timeless... but neither can you believe him omniscient in a strong sense, immutable, or omnipotent, so basically can't believe in anything resembling a coherent doctrine of God.