No, it may not be everyone's cup of mushroom tea, but more fool them. This is the most original piece of film-making I've seen for years and I found myself so utterly gripped that when the Film4 premiere finished I immediately flipped over to Film4+1 to watch the last hour again.
While unlike anything you'll have seen before, it does evoke other distinctive and ground-breaking films you probably know - lots of British cult and art-house cinema for sure (including Lindsay Anderson's If) but also influences from much further (ahem) afield. Something in the interplay of cinematography and score brings Leone/Morricone to mind in places. There are visual cues, too, that surely reference the Hollywood western while maintaining a strikingly British feel (for example in its lunatic humour and its commendable preoccupation with pubs).
And if there's a lack of coherence (hallucinogenic experiences - in reality or representation - aren't exactly renowned for strong linear narrative) then there's an aesthetic unity to this film that marks it out as something special. That unity is also strongly felt in the score, the trailers on Youtube and on the Rook Films website, and the poster and other artwork (something tells me that poster will be plastering student accommodation up and down the land very soon).
Very highly recommended if you've a taste for off-beat, British, hallucinatory, sometimes violent, sometimes dementedly funny English Civil War films set in fields. And very highly recommended if you haven't. Like mushroom soup, what harm could it possibly do?