He is known in france as a "war-teller" journalist, with numerous books about WW2, international brigades, anarchism, adventures at sea, normans, french legion... In all his books he is less interested in the justification of the fight than in the heroic fates of the fighters, collectively described as having overcome (or succumbed) to supernatural circumstances.
His book on Napoleon patch up numerous notorious testimonies (Larrey, Coignet, Thiers, Marchand, and so on...). Most of his sources are french, I did not notice any new element in.
The good point his the very vivid style, and that he puts side by side the most epic (Somosierra, cross of the Guadarrama, Ebersberg,...) and the least one (fate of the wounded, Cabrera,...). Thus giving the story of a brilliant legend build upon the suffering and heroism of the numerous ones - centered on the french, it's the story of the Grande Armée, not of the thin red line .
I find him rather fair on the political aspect, with balanced opinion immediately following numerous citations of Napoleon. About the peninsular wars, he is more french-biased, since atrocities are introduced rather like consequences of the half-starvation, or as retaliation for the torture inflicted by guerilla.
More like a good historic novel, with a lot of "épic" collected.
Sincerely,
Jean