not bad

Also, not half bad; not so or too bad; not too shabby. Fairly good, as in Not bad, said the conductor, but we need to play the scherzo again, or The movie wasn't half bad, but Jerry wanted to go home, or Our garden's not too bad this year, or How are things going?--Not too shabby. All of the terms involving bad, which imply that something is less bad than it might be, date from the mid-1700s. The last variant, using shabby in the sense of "inferior," is slang of the late 1900s.

The adjective has one meaning:

Meaning #1: (informal) very good
  Synonyms: bang-up, bully, corking, cracking, dandy, great, groovy, keen, neat, nifty, peachy, slap-up, swell, smashing