When you say partial Heretic compatibility, what do you mean? Just weapons working with no special interactions? Specific levels breaking? What?
Sorry for the late reply! "Partial" just applies to what it replaces; it replaces everything that has a Doom analogue, like weapons, but there's still a chunk of things (i.e., the artifacts and enemies) that are left as-is. As far as we know, there's no breakage, it should function unless something was missed in testing.