The term would simply describe something as having the characteristic of humans being absent, i.e. the Moon is currently human-free. As such, it's a value-neutral term.
I can't think of a term along those lines where "-free" isn't supposed to sound positive: proponents of "gun-free" or "drug-free" zones don't think that guns or drugs (in general) are good things.
I've seen the term "content-free" used to describe a book or movie that's devoid of information, so there's a negative example. The term "context-free" is neutral. The term "sugar-free", while sometimes used as a positive in advertising, can also have be used negatively ("of course it tastes lousy, it's sugar-free"). The term "value-free" is used both positively and negatively.
Oh, I've always seen the term differently and wouldn't use "human-free" if I didn't want to imply some negative side to human inhabitants.
From what I've found online, others (here not talking about you, primarily) would disagree. Even so, I'd still limit my own use of "-free," heh.
I've seen the term "content-free" used to describe a book or movie that's devoid of information, so there's a negative example. The term "context-free" is neutral. The term "sugar-free", while sometimes used as a positive in advertising, can also have be used negatively ("of course it tastes lousy, it's sugar-free"). The term "value-free" is used both positively and negatively.
- I've seen it used negatively too--but in cases when people are simply quoting the term as used positively (in the same way that you and I have heard "sugar-free" used negatively). Maybe I've seen some sarcastic uses too.
- I've always viewed the use of "-free" in "context-free" as sarcastic. Usually I get the sense that people who use it are parodying other "-free" terms and implying that people behind "content-free" stuff consider content a bad thing.
- Yes, in my experience, "context-free" has been generally neutral. I haven't seen it applied to areas where a missing context is problematic or otherwise undesired (of course, your experience may vary).
Even so, again, I generally see "-free" as trying to sound positive about some non-presence. "This car is radio-free" wouldn't make sense to me without some sense that car radios (or something related) are Bad Things.