In slang, über is an adjective synonymous with superior, beyond, surpassing, etc. Über retains the meaning from the language it came from, in this case German.
It can be used as an adverb in order to amplify a verb or another adjective's meaning. In may be hyphenated when used in this sense, as shown below.
Günther's über clock can display any desired information in addition to the time.
Engelbert just got this über-cool video game.