Cornwell is the master of historical fiction and nobody does battles better, but of course he always writes to a formula. As many of the reviews have already said - this is the same old characters - given new names and a different historical era; with the same plot and structure as pretty much all the books Cornwell has written from Sharpe to the Grail Quest series.
All the usual elements are here: the wronged hero, the love interest, the evil protaganist(s) who just seem to heap more and more misery on our hero - and oh yes, a big battle looming.
So the standard Cornwell formula then - but you know what - the formula works! you know what you're going to get - and it's always a thumping good read.
Azincourt leans heavily on the excellent non-fiction account of the campaign: Agincourt: The King, the Campaign, the Battle
- which I highly recommend for further reading. But if you want a good page-turning novel, which will give you an excellent overview of the Agincourt campaign and battle from a soldiers eye view - then read Cornwell's Azincourt.
As this book covers Soissons, the march to war, the seige of Harfleur and the Battle of Agincourt itself - in exquisite and gory detail - I think it could easily have been padded out into another trilogy - but Cornwell manages to capture it all in this one book, and for that reason I think Agincourt ranks amongst his very best work and almost certainly his best standalone novel.