This isn't as bad a movie as many critics and viewers who write critiques have made it out to be, but isn't anything like a blockbuster that hasn't been matched or bettered before. Nice summer movie to watch when the heat wave breaks and you have a long rainy day. I have several complaints, but I'll start with the virtues:
It was well filmed, with good settings (although there is nothing like those Alpine mountains in Britain, except maybe in the Scottish Highlands during mid-winter). The battle scenes were fine, except to the extent they were toned down to get the PG rating (wait for the DVD) -- especially a really good one that takes place on the surface of a frozen lake. The depiction of Hadrian's Wall and its ancillary fortresses and villages -- with taverns and hooker joints -- was archaeologically and historically accurate, even if the purported site of the Battle of Badon is imaginary (could be presumed to be modeled on Housesteads combined with Vindolanda). And yes, the Romans did have draftees in the legions from other parts of the Empire in posts like the Great Wall, and they were inducted for 15 to 20 years before being granted civilian status and pensions. That Arthur's traditional knights were Sarmations, we'd call them Ukrainians now, has to be taken with a grain of salt. In these senses, the movie is a good approximation of the latter days of the Roman Empire in Britain, but it certainly doesn't break any new 'archeological or historical ground'. I have no imaginative problems, as some people with that kind of interest do, with the technology of the battle scenes -- the Romans had catapults and naphtha bombs (Greek fire), even if they were unlikely to have been used in the sort of battle shown here against a marauding horde of barbarians, and manned by another horde of barbarians, those so-called Picts who become Arthur's allies.
Doubtful elements: As I said, the Ukrainian Knights -- and in fact I was fooled into thinking the kid drafted from the steppes to join the Roman cavalry was supposed to be Arthur, but turns out to be Lancelot, and well, that just won't do. First of all Lancelot was French, an interpolation from the Middle Ages. Galahad was also a Norman French invention. The more traditional Arthurian characters, going back to the original Welsh legends, as close as we'll ever get to historical 'reality', were Gawain and Bors -- who were certainly not Ukrainians! Tristan or Tristram has his own mythology, involving the Irish princess Iseult, as we know from Wagner's opera and other sources, so why is he killed off before he can accomplish this? (Besides, it is Gawain who supposedly had a connection with hawks, not Tristan, and is also said to have killed giants.) It is likely that the historical Arthur was a Roman officer, perhaps related to the historical Ambrosius Aurelianus, who commanded a 'rapid reaction force', and in any case was definitely British -- that all fits. What the screenplay doesn't explain at all, probably because of very poor editing, is that bit about the sword in the stone and the burning of the young Arthur's house by raiders led by, presumably, the British (Welsh) Merlin, who by the way was not a PICT. Here I was, thinking he was the kid from the steppes, then all of a sudden we get this thrown in, and was that really supposed to have been his father who broke the ice on the lake to drown the Saxons, at the cost of his own life? Say, what? Where did this come from out of the blue? Cerdic and Cynric, the Saxon leaders, were definitely historical characters, but they were the founders of WESSEX in the south of England and had nothing to do with the Saxon invasion north of the wall when the Northumbrian kingdom was established.
Totally wrong and misleading elements: Even the historical sources mention several great battles of the Britons against the Saxons and Scots, which took place over several years, led by a great war leader. Many of them took place in Lowland Scotland and the Border country, but the famous battle of Mount Badon is generally considered to have taken place south west of London. Hadrian's Wall had been abandoned several years before. There was no one great decisive routing of the invaders before Badon. The so-called Pelagian heresy took place before these times and is one of those silly arguments whereby Christians killed other Christians over trivial matters -- the Victorians made Pelagius into a hero because he was British, but as far as I can figure out, his 'heresy' had nothing to do with Freedom and All Men Are Created Equal. Arthur is more likely to have been a Mithraist, like other legionaries, even if nominally Christian.
As for the script, all I can say is that it is muddled beyond easy comprehension. That could have as much to do with the way the film was finally edited as with any original deficiency, even granted that it is not a strong script to begin with. The acting is generally very well done -- again allowing for the fact that the roles and lines were chopped up for whatever reasons. One very laughable bit concerns the lovely Keira (Guinevere), who is rescued from a dungeon where everybody else has starved or been tortured to death, has Arthur treat her maimed hands, then a day or so later is an Olympic class archer. 'I see your fingers are better now,' says Arthur.
