If you're unenthused about something, you're not particularly interested in it. It's understandable to be unenthused about watching The Little Mermaid with your younger brother for the fifteenth time.
Being unenthused doesn't necessarily mean intensely disliking something; it's just not being able to work up any enthusiasm about it. Unenthused (along with enthusiasm and enthusiastic) is rooted in the Greek entheos, "divinely inspired or possessed by a god." When your feeling about a situation or activity is the complete opposite of inspired, you can say you're unenthused: "The whole class is pretty unenthused about the upcoming field trip to the envelope factory."