What's a word that has the half-positive, half-negative denotation of half-hearted but none of the unenthusiastic connotations?
I think neutral may suggest the half-positive and half-negative connotations of half-hearted without a negative bias:
- of no distinctive quality, characteristics, or type.
- A half-hearted smile; a neutral smile.
The Free Dictionary
Perhaps of two minds
undecided; wavering: he was in two minds about marriage
I have only personally heard the of version. The in form has apparently diminished in usage in the later 20th century in the US according to ngram plots. In British English, the reverse seems true according to ngram.
(especially of a liquid) only slightly warm; lukewarm. synonyms: lukewarm, warmish, slightly warm; at room temperature "tepid water"
showing little enthusiasm. "the applause was tepid" synonyms: unenthusiastic, apathetic, muted, halfhearted, so-so, 'comme ci, comme ça', indifferent, subdued, cool, lukewarm, uninterested, unenthused "a tepid response"
from Google's definition
Because tepid's primary meaning is a literal one related to water, it has very little positive or negative connotation because people generally don't have strong emotional commitments to water temperature.
I feel that indifferent is a good word for this request.
Indifferent via Webster's