I think this is one of the most poignant chorale preludes I know. Brahms didn't intend it for publication; it's probably one of the last pieces of music he wrote and he knew that the end was near. We (or, at least, I) mainly associate the tune with "O Haupt voll Blut und Wunden," but, in fact, the mood of the words of "Herzlich tut" is actually very different: the writer is actually looking forward to death, which is why the last chord is sometimes played as a "tierce de Picardie." I hear the pulsing bass as a heartbeat which, a whole three (long) bars before the end, slows and finally stops altogether. I half expect to hear a long high note at the end like a heart monitor alarm!
I find it very odd that his other setting of the same chorale in Op122 is so different.