In A Visit from Verin Sedai, Verin says something interesting: "The Chosen are predictable, but the Great Lord is anything but. Even after decades of study, I can't be certain exactly what he wants or why he wants it. I only know that this battle isn't being fought the way that al'Thor assumes it will be." This got me thinking A) What is the true battle the Dark One is fighting, B) why is it fought this way (and not a traditional way), C) what does this imply about the Dark One's motivations, and D) what is the nature of the Dark One's prison. Here are my theories.
A) It seems obvious to me that the "Last Battle" is irrelevant. In my opinion, the most important battle has already been fought by Rand and won. This battle lasted since near the beginning of The Eye of the World and ended when Rand "won" in VOG. What do I mean by this? I do not believe that the Dark One wished to kill, capture, or convert Rand. Many of us (including me until recently) believe that the forsaken are/were dangerously incompetent, but were they? What if their mission (unbeknownst to them) wasn't to kill or capture Rand. Alright, granted they were ordered not to kill him (Semirhage was even ordered to save him by sending trollocs to the Stone), but I don't believe they knew why this order was given (and many planned on ignoring it, such as Granedal, Demandred, Aran'gar and I believe Mesaana). I believe that the battle was for Rand's soul. If the Dark One's mission was to force Rand to become so depressed that he wants the world to end, then his forsaken and other minions were wildly successful. Simply consider how close to destroying the world Rand came in VOG.
B) The natural question that follows from this theory about the Dark One's behavior is why? Why does the Dark One not wish to kill or capture (and convert) Rand? I would like to point out quickly that I believe it is obvious the Dark One did not wish to capture Rand. He could have denied Rand access to the True Power, and blam he would have been captured and 13X13'd. I believe the Dark One set free Semirhage and gave her the domination band in a complex plot to force Rand to use the True Power. Why? To further his goal of making Rand more depressed and deprived. It is clear that the Dark One did not want Rand dead or captured. All of this speculation, is however, redundant. Consider what we learned in the Great Hunt when Rand travelled by portal stone. The Dark One has tried AN INFINITE number of times to "win." I will discuss what he wants to achieve later, but first let's consider this fact. A wheel has no beginnings...so the Dark One has fought, and lost, a huge amount of times. He must have tried everything. According to the portal stone visions, he did try everything. And yet, the world still exists. Apparently, killing Rand early, capturing Rand, and killing him at the "Last Battle" all result in the Dark One "losing." We also learned this from Herid Fel (who was killed for learning this, lest he let Rand know. The Dark One needed Rand to be focused on fighting the forsaken and for him to be ignorant of the true battle the Dark One was waging). I believe that this turning of the wheel that RJ has presented us is unique. The Dark One has finally stopped trying to kill or capture Rand and he has attempted to force Rand into a state of absolute despair. Why? I'll answer that in part D.
C) So what does the Dark One want? I believe that he simply wishes to destroy existence. The complete end of all things. The Dark One is not human and as such cannot have human motivations. The Dark One is a force of nature that simply wishes to destroy. Only Moridin (and myself, of course :) is aware of this fact: "'There is no path to victory,' Moridin said. 'The only path is to follow the Great Lord and rule for a time before all things end. The others are fools. They look for grand rewards in the eternities, but there will be no eternities. Only the now, the last days.' He laughed again, and this time there was joy in it. True pleasure" Moridin wants existence to end as well. Only he understands the Dark One, and therefore he is Nae'Blis. My third theory is that the Creator made the Dark One in order for death to occur. It is obvious that without death life cannot exist. The Creator knew, however, that the Dark One would wish to destroy all life and existence, so he imprisoned him. He knew also that someday his prison for the Dark One would be whittled away, no matter how perfect he made it, and he needed a more perfect solution, a perpetual solution, if you will.
D) I believe that Rand's soul is the true seal on the Dark One's prison. I believe the Creator made the Dragon and his soul as a seal on the Dark One's prison. As long as his soul exists, the Dark One cannot destroy the pattern, even if he destroys the world. When the wheel reaches its beginning point, the world pops back into existence. I believe that bestowing this power on the Dragon had one unfortunate side-effect: the Dragon obtained the power to destroy everything. Consider the evidence that shows Rand to be one with the land (the food spoilage when Rand reached the pinnacle of his despair). Rand, I believe, almost destroyed the pattern and all existence in VOG. I further believe that the Dark One took an incredible amount of time to realize this, but this turning of the wheel he tried to manipulate Rand into doing his dirty work. The true last battle has already been fought and won by Rand...assuming Rand doesn't every again touch the True Power or attempt to kill the Dark One. I believe that either of these two attempts will result in a victory for the Dark One.
Alright, let me know what you think (and sorry for the length, I got a bit carried away).