After reading Exodus, it should probably not surprise us that a single book can contain both wonderfully exciting sections alongside mind-numbingly boring ones. Joshua, like Exodus, begins with fast-paced action (Josh. 1-11) and ends with tedium, in this case long lists of land allotments (Josh. 13-21). (In Exodus, we recall the long sections dealing with the construction of the tabernacle.) It makes sense, then, to deal with these two sections separately, as each embody a different aspect of the Bible.
In the first half of Joshua, we come face-to-face with a depiction of the phrase, "going Old Testament." This shows the God of the Hebrews in full force: a warrior god who fights for his people and allows them mighty victories. The Israelites move from one conquest to another, in decreasing levels of detail. The first few victories -- over Jericho and Ai -- are fully fleshed-out, taking at least a chapter each. (Josh. 6 and 7-8, respectively) The encounters with Gibeon and the five Amorite kings who banded together to destroy it are also long and detailed, complete with dialogue. (Josh. 9-10)
However, after Gibeon, the level of detail decreases as the pace gears up to dizzying rapidity. The conquest of the southern kings in the latter half of Josh. 10 is formulaic, with each city getting only two or three verses. Though there is some set-up to the conquest of the northern kings in Josh. 11, most of the conquest comes down to a single verse: "All the cities of those [northern] kings, and all the kings of them, did Joshua take, and smote them with the edge of the sword, and he utterly destroyed them." (Josh. 11:12) In the next chapter, Josh. 12, we get a list of the 31 defeated kings, of which we only have a detailed account of two.
No doubt there were equally interesting stories for the conquest of the southern and northern kingdoms, but the text neglects to mention them. Instead, it apparently reasons that a few examples (Jericho, Ai, and Gibeon) should be enough to get the flavour, and afterwards only a list of the defeated cities is required.
This ties neatly in with the second half of the book, which consists mainly of land allotments. These chapters are detailed, precise, formulaic, and mostly devoid of any sort of narrative. They list the various tribes' land allotments one after another, sometimes tracing boundaries and sometimes only listing cities. Even the Levite towns are merely listed with little idea of their qualities.
This is because, in the end, Joshua is the foundation book for the Israelites living in Canaan. Unlike the Pentateuch (Genesis through Deuteronomy), Joshua is not a mythology book. It is not a cultural binding, not a cultural memory, like the stories of the patriarchs, the parting of the Red Sea, or the wanderings in the desert. Instead, it is a reference book. We can imagine that it was used by later generations when there was some dispute about which tribe owned which piece of land or which city. It needed to trace precise borders for just this reason.
It did not, however, need to provide yet more cultural history about the mighty Israelite conquests. A few stories for good measure, which could be used by the storytellers to describe the prowess of the Israelites and expound the glory of God, would be sufficient. No doubt there were stories circulating for quite a long time about the various other cities the Israelites conquered, but they were not important enough to be recorded.
The few piece of true narrative in Joshua -- the conquest of Jericho and Ai, Gibeon's deception, the eastern tribes' altar -- all serve to illustrate some ethical principle about worship. The conquest of Jericho shows both the importance of relying on God and the mighty conquests that the Israelites can achieve if they follow him. The conquest of Ai, on the other hand, shows the punishments that will result from not following God. Finally, the eastern tribes' altar demonstrates that there are ways to worship God which might not be immediately apparent: the western tribes assumed the new altar was a form of idolatry, when it was in fact a new form of worship.
In the end, Joshua is a book of tying up loose ends. By the end of Joshua, Canaan has been conquered and the Israelites are all installed in their various tribal lands (or cities, for the Levites). God brought the Israelites back to the promised land, just like he told Moses in Exodus and the patriarchs in Genesis. Now all that remains is for the Israelites to actually live according to God's law, which is apparently a lot more difficult than we might originally think, as we shall see in the book of Judges, starting tomorrow.