I feel like we were let down on the "why" of why he did it
Because ultimately, that seemed to be the question that needed to be answered...especially during the last few episodes when it seemed pretty likely it was the husband.
So why would this seemingly successful, family-oriented person suddenly snap into a monster capable of demolishing the hell out of that woman's skull.
I expected some extraordinary...something, but it seemed like they just had a bit of a spat...and she grabs the hammer...and that was enough for him to unleash hell and obliterate her head.
That whole scene was just kind of disappointing...there didn't seem to be any real passion there, no real palpable anger, let alone fury.
She seemed to pick up the hammer almost casually...it was weird, and then that was the conduit, I guess.
The whole scene felt forced IMO. Maybe I'm missing something, but finding out why he did it was pretty unsatisfying.