unreal (adj.)

c. 1600, "not real," from un- (1) "not" + real (adj.). Meaning "impractical, visionary" is by 1660s. Slang sense of "wonderful, great" is first recorded 1965.

Unreal City,
Under the brown fog of a winter dawn,
A crowd flowed over London Bridge, so many,
I had not thought death had undone so many.
[Eliot, from "The Waste Land," 1922]

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Definitions of unreal from WordNet

unreal (adj.)
lacking in reality or substance or genuineness; not corresponding to acknowledged facts or criteria;
unreal propaganda serving as news
ghosts and other unreal entities
unreal (adj.)
not actually such; being or seeming fanciful or imaginary;
the fantastically unreal world of government bureaucracy
this conversation is getting more and more unreal
the unreal world of advertising art
unreal (adj.)
lacking material form or substance; unreal;
unreal (adj.)
contrived by art rather than nature;
Synonyms: artificial