"I'm less than impressed"

• Verbal shrug
• "So exciting--not"
• Modern slang word suggesting apathy
• Utterance of indifference
• "I've seen better"
• Unimpressed reaction
• 'So what?'
• Just so-so

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
expression of apathy or indifference, by 2003 (perhaps from 1992).

Wiktionary Word definitions in Wiktionary
a. 1 mediocre; lackluster; unexceptional; uninspiring. 2 apathetic; unenthusiastic. interj. (context slang English) (non-gloss definition: Expressing indifference or lack of enthusiasm.)