I have just finished reading the Waterloo section. On the whole I found it quite interesting, although the military talk occasionally went over my head.
In terms of what the section was trying to say, I would suggest:
1.War is awful. I like Hugo's description of the richness of life and how it can be taken away in a moment on the battlefield.
2.History is not made by great men who win great battles (see the Great Man theory http://en.wikipedia.org/wiki/Great_Man_theory
which was popular at the time). Tolstoy makes this point too throughout War and Peace.
3.The result of Waterloo, and other historical events, was not inevitable. This is contrary to the Whig view of history (see http://en.wikipedia.org/wiki/Whig_history
4.Destiny (or God or the Infinite) is ultimately in control. A non spiritual person will of course dispute this but Hugo does seems obsessed with the idea of destiny and fate. This is probably why a lot of the novel relies on coincidence.
5.The more things change, the more things stay the same. Napoleon promised liberty but became a despot himself. After the downfall of Napoleon many monarchies promised reform but failed to deliver. The result was a return to the old political system pre French Revolution.
6.The people and culture of a nation should be the source of its greatness, not its military prowess.
I like the way the final chapter ties the Waterloo narrative into the narrative of the main story. I wasn't expecting that.
What do others think?