Series 1: https://youtu.be/1uJt4cu8zw8
Series 2: https://youtu.be/8XvFO83LXBE
I cannot recall if I read either the original graphic novel first or saw the film version, but I do know that when I came to the second form, I felt that both versions were equally effective. If I read it first, then the series seemed true and faithful and the slight degree of expansion was effective, while if I saw it first I thought that the written version was marvelously stylishly original and that elements of that were caught in the filmed version. The original novel had a leanness that the filmed version could not really take and because of its minimalist visual style, the focus was utterly on the words and actions of the two central characters. With the film there was not really a visual equivalent of this - I am not sure how there could be tbh but in any case the combination of black humour and sympathy for two remarkably apparently unsympathetic characters came across powerfully in both versions.
I have slightly more reservations about the second series. The book( as with Series 1) had an ending which on one level could allow for development but the stark suddenness of it was its greatest strength and I felt, certainly when reading the novel, that I could accept that that was it. So when I saw there was a second series I was intrigued. There was a radical decision made to enable it to continue but finally I felt that there was, essentially, a re-treading of the ground we had already gone over. Cannot say too much as that would be major plot-spoiling, but if you have seen it you will know what I mean…I think.
Also the stylistic traits of the first (long shots/slow editing/silences/ironical or painfully appropriate use of contemporary pop songs) were all used but here I felt it was getting too mannered and obvious - particularly with the songs which by the end of this second series were simply irritatingly obtrusive.