Nick Drake was incredible; everyone who's heard him play will agree. "Five leaves left" was his first album, and was promptly ignored by critics and consumers alike upon its release; only relatively recently has his talent started to be properly realised. This is definitely English folk music, but equally has definite jazz, blues and occasionally classical nuances; given that Nick was a public-school boy, it's perhaps not so surprising that his deep, resonant voice has more than a little of an upper-class English accent.
Most of the songs on the album are accompanied by Nick on acoustic guitar, and many of them have string arrangements by his friend Robert Kirby. Nick's guitar playing has attracted attention from just about everyone; it was rare for him to write any song in a conventional tuning, and the work he put into retuning the instrument is apparent from the big, open sounding, slightly jazzy voicings you can hear throughout the album (Incidentally, I hate to be picky, but another reviewer says that he played 12-string guitar; he only ever recorded with one guitar, a Guild M20 six string acoustic).
I suppose the best way to describe the tone of the album would be to use the word "wistful"- there's no out-and-out depression here (as can certainly be heard in some of his later recordings), but sadness permeates all the recordings at some level. It's a hopelessly romantic, dreamy, incredibly beautiful album; anyone with a soul cannot help but fall in love with it.