I'm Welsh, so forgive me if I fail the US spell-check.
Firstly I'm bewildered, amused and dismayed by many of the comments: "Funny British Accents" (they're English accents), followed up by "Would be OK in Trainspotting II" (which is a Scottish film with Scottish accents), yes there are three countries in Great Britain. It's not called Great because it's great, it's to distinguish it from Brittany in France, formerly known as Little Britain after some Britons fled the Saxons and colonised the area. There's a bit of history for you.
Then we get into the historical accuracy of it all... and "Vikings" is held up as a better example, when most of "Vikings" is historically wrong.
Unlike "Vikings" this is a fantasy, it's not supposed to represent history, it's also not a Hollywood film, it's a "British" (English) one, that's why everyone talks with a "Funny British Accent".
There's also a fair amount of Old English and a snippet of Old Welsh, I don't think I've heard those languages used on film before.
It's main flaws are in trying to pander to the U.S. market (make it simpler and dumber)... yet it has strong performances throughout, a great lead in Charlie Bewley, fantastic settings, a solid although somewhat bipolar score, solid cinematography and a half-decent script.
People lap this stuff up in Game of Thrones yet as soon as you fix something which is obviously a fantasy to a point in history it get's pulled apart?
It's a solid 7. I'd have given it a 6 yet I find my patriotism roused by indignation at ignorance.
If you want to find something that completely lacks historical accuracy, only happened a couple of hundred years ago yet is revered as a great film, please watch Lincoln.