What is a word for "someone who doesn't share the same enthusiasm"
Solution 1:
From an Oxford entry:
unenthused (adj.)
not interested or appreciative
You appreciate your exam grade, but he doesn't.
Solution 2:
I appreciate that an answer has been selected, but just to add an option for others, I would suggest indifferent. (M-W)
Solution 3:
Aloof - adjective - Conspicuously uninvolved and uninterested, typically through distaste.