Marvin Gay’s signature tune, with a weird recording and release history (check Wikipedia for details). Million seller for Motown in two different versions - the other one is a completely different up-tempo arrangement by Gladys Knight.
With this tune, the soul groove is most important. Lots of open strings in the chosen key of E minor, which give you some freedom for improvisation. To spice it up, you can add some thumb slaps on beats 2 and 4 or play the bass in straight quarters on the lower bass strings (instead of the alternating bass noted). Trickiest part is the end of bar 4 in part [ A ], with the jump up to the 12th fret. The end of the chorus [ B ] might as well be played one octave up.