倍儿 (super) + 爽 (refreshing / pleasurable) = the archetypal Beijing compliment for food, weather, or a good experience. Feels more visceral than 特别好 — 爽 carries a sensory, body-feels-good charge.
Singer-songwriter 大张伟 performed 倍儿爽 at the 2014 Spring Festival Gala; the chorus 我的心情倍儿爽 became a nationwide catchphrase and pushed Beijing 倍儿 slang into everyone's vocabulary overnight.