they are based on Hack n slash games that are based on the warrior states period. Sengoku Basara is more over the top and intentionally historically inaccurate, where as Sengoku Musou is more focused on the historical side of the period.
these Anime's know the way of the samurai. if you love historical anime with ninjas and samurai warriors then this is for you. the fighting skills and spirit of the warriors within these anime's are very similar and unique; the only difference being sengoku musou does not have a supernatural element to it like donten ni waru.
Both shows tend to go quite deep in the politics and war with quite lengthy explaining of the strategy used. Main difference is that Madan no Ou to Vanadis is harem/fantasy action, while Sengoku Musou is a historical fantasy action.
On the bad side - both shows have quite mediocre animation and visuals, with characters going off-model pretty often. Sengoku Musou is a little better on this direction, though (no weird dancing from the soldiers has been spotted and there's less slide-shows).