I'm a history major. These Osprey books seem to be of universally high quality, especially considering that they are intended for consumption by laymen. I own quite a few of them, I'm keeping them for my kids, but I find them fun. I would rate them higher if they listed the sources they reference (so I can backtrack their research) but this is rare in general market books. The plates are generally pretty accurate, there have been some minor inaccuracies (some of which I've found pointed out in the text). I would mainly offer them to smart kids around middle school as they can be a fun way to learn about ancient warfare, I think the pictures are mainly to keep the attention of a mainstream audience that includes kids and young adults. For that purpose they excell as they have much more meaty info than the other "illustrated history" books.
Regarding a previous review by that russian guy who accuses historical inaccuracy. I can't comment on the fashion choices as medieval fashion is definitely not my area, but European martial arts/history is my specialty. That "slashing spear" is called a glaive and it *is* historically accurate. Unlike the naginata used by the japanese which has a tang that extends into the haft, the glaive is affixed via a socket like an axe head. There were a wide variety of bizzare polearms in use at the time, including similar arms like the voluge, berdiche, glaive-guisarme, and halberd. Check your facts, dude.