The middle three chapters of Hasker's superb treatment of God and evil center largely on the natural world. He has, at this point in his argument, established that it is logically compatible to accept the premise of a divine creator alongside the existence of evil in the world. However, he sets forth to move forward from this, "Mere logical compatibility, however, falls short of what theists wish to affirm and of what is demanded of them by their critics" (74-75). As a caveat (and a critique) of how much of this topic has been handled, he offers: "Now, however, I want to suggest that a book about the problem of evil should not be focused too exclusively on evil" (75).
One of the issues which Hasker raises in Chapter Four is whether or not God created the best possible world, specifically dealing with the philosophy of Leibniz and William Rowe (the latter claims that if God does not create the best possible world then he cannot be considered morally good, cf. 76). The argument given here challenges the notion of a 'best possible world' on a few levels, the most intriguing for me being the question: "If God is perfectly good, does this mean that he must, of necessity, create the best possible world?" (78). This exposes a larger issue - that too much theologizing is stripping God of his freedom in creation. Furthermore, problems abound when we try and determine or measure "best" in relation to creation (78-79).
What would work well with Hasker's approach here is the hermeneutic employed in Goldingay's Old Testament Theology, v. 1 - especially the emphases given to God's ability to create in his own freedom. And it is precisely the point of free-will theism to say that God has given away his ability to control every aspect of his creation, thus "If God creates a world with this kind of freedom, then he voluntarily gives up part of his own power to determine how things go in this world" (80, emphasis in original). An interesting challenge which Hasker discusses comes from the concept of grace, which has often (I have heard this in many forms) put forth the argument that God must have created an imperfect world (ordaining a fall) in order for him to demonstrate his grace. But, as Hasker defends more fully, the concept of grace is necessarily a response and cannot be a reason for an action (e.g. 83f.).
In understanding creation, Hasker provides a basis for moving forward to a discussion of why evil occurs. Theological determinism is weak on these points (I believe) and has difficulty in capturing the essence of Scripture. "This [theological determinism] contradicts a great deal of what is said in the Bible, which repeatedly and emphatically insists that many things are not as God wishes them to be" (93, emphasis in original).
Chapter Five then deals with the question, 'Is the world cruel?' Hasker begins with an evaluation of Dembski's rather odd reading of Genesis 1, appropriately challenging it and eventually exposing its serious contradiction. One of the gems given in this chapter is the statement, "What often prevents us from taking this enlightened viewpoint is our natural egoism, in which we see everything from the standpoint of how it affects us personally" (111).
The chapter sets forth Hasker's claims:
1) it is good that there should be a world (122).
2) it is good that there should be a complex, multileveled natural world (123).
3) it is good that a world contain living beings that are sentient and rational (124).
4) it is good that the creatures in the world should enjoy a considerable amount of autonomy (124).
5) it is good that there should be an evolving world, a world in which the universe as a whole as well as its component systems develop from within, utilizing their inherent powers and potentiality (125).
In a (very small) nutshell: What causes natural evil? The laws of nature, mostly. Is the world cruel? "The world is not cruel, for it lacks the capacity to be cruel" (133).
From here, Hasker moves toward and presents a natural-order theodicy (cf. 138), which focuses more on the ability and freedom of God to create than it does in the personal experience of the individual who has experienced pain, suffering and evil. So, could God have created a world in which we don't have this suffering (if so, why didn't he)? This is ultimately is unanswerable and should not be speculated, less we stray from a correct biblical understanding of God. This is important to Hasker throughout the work (and I commend him for it in light of the current divides between philosophy and systematic theology and biblical studies), who notes Job 39 and Psalm 104 and their unembarrassed record of all creatures made by God - even the dangerous ones (e.g. 139).
One further note: In Chapter Five Hasker relates these issues with the Jewish concept of Tzimzum. While he does not necessarily subscribe to the theory, he does find some good food for thought in the concept. Fundamentally, the idea is that God cannot manifest himself in his full glory lest the world be overwhelmed and destroyed because of its greatness. Therefore he has 'withdrawn' his glory and granted 'autonomy' to his creation in order that life may exist and move forward as he desires. Although there are certainly some holes which would need filled, this is an interesting perspective which comes into play at this point.