Steve Muhlberger's review pretty much agrees with my own impressions. The recreated world seems very real and richly detailed even though an informed viewer can spot anachronisms. A lot of the action is set against sweeping panoramas of medieval landscape and seascape. This is a movie that benefits from a big screen.
Eleanor of Aquitaine, William Marshal and Richard are portrayed well and with reasonable fidelity to their historical character. It's great to see the Marshal finally get a major role on the big screen. (His portrayal in Lion in Winter was spot on in showing his competence and value to the crown, but he didn't get a lot of lines) Bad King John is complexly bad. Isabella of Angoulême, John's hot jailbait second queen, has a more interesting role than I expected.
I can forgive most of the anachronisms as driven by dramatic or practical reasons rather than carelessness. The visored or open faced sallets sometimes worn are from a later era, but convey knightly status and allow characters' faces to be revealed or concealed as needed. Glazed windows are anachronistic, but it looks like Ridley Scott found an existing building to shoot in, and removing the windows for the shoot would have been an expensive process.
Although ramped landing ships were used in this era, the landing craft in the film look too much like WWII Higgins boats. Recreating the big galleys actually used would have been tremendously costly, let alone training the extras to carry out the difficult stern first beaching.
The anachronisms and ahistorical moments were not intrusive enough to stop me from enjoying the film a great deal.