His most famous work is the "The Face of Battle", which attempts to put a human face on descriptions of warfare (specifically Agincourt, Waterloo and the Somme), and does a fairly good job of that.

The main criticisms of him that I'm aware of is a fairly unswerving pro-British bias - he rarely if ever criticises British military efforts, and usually found a way to spin the apparent negatives (say, the Somme) into net positives.

To use that example specifically, his argument for the development of tactics during trench warfare focuses more on the extremely sophisticated artillery techniques that had been developed, but does gloss over the extremely unsophisticated infantry techniques that were in existence at the same time - essentially boiling them down to them being necessary.

That's an arguable point to begin with (it's not necessarily wrong), but you can generally guess what side of an argument he will come down on.