Entanglement is functionally very similar to Tikki's Learning boon if used properly, and is practically free.
The 5 piety is often worthwhile just for a first-strike finisher against a single monster, forget the fact that the effect hits the entire dungeon floor
. Very good boon and one of the main reasons to hop into Earthmother's religion.
The problem is that Earthmother is extremely map dependent. I compared Vineform to Absolution, but Absolution clears hallways whereas Vineform cramps them. This is tolerable in some maps and disastrous in others. If you could prep ENDISWAL she would be good on any dungeon, but you can't so she isn't.
This I wholeheartedly agree with. Earthmother is a disaster waiting to happen on cramped maps.
Her other issue is that unlike all of the other deities, Earthmother doesn't have a single enduring OMGWTFBBQ power that you can dip into her religion to seize. This is probably deliberate, since piety is so easy with her. All the same, I wouldn't mind some kind of 80 piety mega boon for her, but that's just a pipe dream.
Spend 80 piety on clearance and it sure feels like a OMGWTFBBQ superpower. It's getting enough plants on the field to do this that's the challenge.