Like the books of most of the Old Testament prophets, Isaiah strikes me as disjointed, and I think the reason is that it is not a single narrative, but apparently a series of sermons preached at different times. Nevertheless, there seems to be a general theme. Many of these sermons deal with the fate of nations, of Israel and its neighbors. Isaiah speaks of their sins and of God's judgement upon them, and then of his mercy and forgiveness and restoration for a repentant Israel.
In the midst of these themes, you occasionally notice something a bit curious; something in the text that strikes a slightly discordant note - a promise, perhaps, that appears too lavish for the topic at hand. Odd... as if you were on a boat and noticed a curious swelling in the sea. But then the swelling subsides and the sea returns to normal.
And then, at other points, a beautiful transcendent passage flashes out of the narrative - sometimes for just a second - stunningly unrelated to the apparent topic, and then is gone again, like a jumping fish diving back into the ocean.
As you read, it becomes increasingly clear that Isaiah is about something even greater than the rise and fall of nations. There is something mysterious going on beneath the surface that occasionally breaks into the open. Sometimes you see messianic hints which seem, well... doubtful, blended, as they are, with other topics to the point where they are merely suggestive (Was it just a peculiar current? the reader may ask, or was there really something there under the water?). But at other times the messianic promises simply leap out of the water, flashing clearly in the sunlight, often at unexpected moments in the text.
And toward the end of the book the New simply breaks out with wild abandon - with long messianic passages, such as Isaiah 53, wonderful promises, and descriptions of a new world. The fate of nations is almost forgotten in its glory. It reminds me of the Bible as a whole - the hints and explicit prophesies of the Messiah in the Old Testament, followed by the glorious reality of the Messiah in the New Testament.