Louis C.K. ruffled feathers with his last surprise set in NYC -- some audience members called his appearance an "ambush" -- but Sunday night the crowd showed him nothin' but love.

Louis was introduced at the famed Comedy Cellar in Greenwich Village -- the same place he popped up in August -- and it must have felt like old times for him. The Hollywood Reporter says it got this audio of his intro ... which brought thunderous applause.

Listen to the reception Louis C.K. received when he returned to New York's Comedy Cellar for another surprise set late Sunday night: pic.twitter.com/7uBw846xIX @THR

There's a lot of cheering and whistling here, and you eventually hear Louis thank everyone.

As we reported ... reactions to Louis' return to stand-up has been mixed, with some embracing it ... and many others saying it's too soon just a year after his sex scandal.