Ending was too safe and rushed imo. It's a case of either having a good/great tragic ending of growth and self-reflection vs an average/okay feels good happy ending with happy feelings only. I personally would have preferred the heavily implied "bad end" because it would have left room for a lot of growth for the older sister (and well, artfully avoid the incest ending while still indulging in all the incest themes throughout the story), but probably a lot more people would have preferred a happy ending without any bad loose ends existing at the cost of the ending being just okay not great.
A lot of plot points ended up getting resolved extremely quickly or completely left open, probably because of the axe. The B-Story couple just sorta ended with them hanging out not really confirming their relationship, the dad gets a final one-liner that really isn't expanded further (and they're all okay now and all living together soon), yandere childhood acquaintance is now a redeemed friend but is never touched upon again, it's never explained why Oga can see angels, and the entire main conflict hinted back all the way from chapter 1 with the little sister being an angel is wrapped up in pretty much 2 chapters. Could have really used another volume to dive into these more but I can't blame Itou-sensei for that.