I had always taught and thought and heard that english R must sound as if one try to say russian R while having a porridge in his mouth.
Though recently I've got an audiobook "The Lord od the Rings" where the true british actor read the text and often says R almost in the same way as we do it in Russia. Not only in the words of elvish tongue or one of Mordor but also in some english words.
The same matter I heard on TV in some british performance fragments by Shakespeare.
Besides I've heard in some songs of Pink Floyd they speak having R's rolling as if they take off someone.
So my questions are:
How english R may sound in all the possible cases?
How may it's pronounciation depend of local dialects?
Should I persist in R prononciation or maybe it's not very important?
Does it look too queer to speak english using russian pronounciation of R?
Did I wrote properly all above? You are wellcome to point me my mistakes.