The Gemara’s terminology is ????? ????? ???, so it would seem to be obligatory, and, of course, this is how it is understood by Shulchan Aruch. It seems to be a ???? ????? (as opposed to a ????, the implication of the Chafetz Chaim’s wording notwithstanding).
Although there is no specific ???? prescribed for one who violates even most ????? ??? ?? ????? (of course, as is well known, ??? and ???? are the exceptions to this rule, as failure to fulfill either of those ????? carries a punishment of ???), it is clearly an ????? to do so (as evidenced by the famous Gemara about ????? ?? ???? ????? and the Yerushalmi regarding failure to fulfill Tzitzis ????? ?????, among many others), since the concept of ????? is simply transgression of the ???? ???. This is clearly true of anything accepted by Halacha as Ratzon Hashem, regardless of its origin.