AllMusic editor Tom Demalon described the song as a "massive, neo-hippie anthem" in his review of
Bigger, Better, Faster, More! Rolf Edmund Lund from Norwegian
Altaposten complimented Perry's voice as "incredibly good".
Larry Flick from
Billboard magazine wrote, "Gymnastic vocals, leaping from a breathy, high range, to gravelly, bar-rock blues in a single passage, front this straightforward, heartfelt rocker. Treads the line between album rock and modern rock, with the piano version favoring the former." Tom Sinclair from
Entertainment Weekly described it as "funky" and added that it "is only one of the goodies in the Blondes' musical grab bag". In his weekly UK chart commentary,
James Masterton viewed it as "a wonderful piece of laid back summer rock (well, almost)". Pan-European magazine
Music & Media complimented it as a "strong composition", where the lyrics "are done more than justice by Linda Perry's impressive vocal touch." A
Music & Media editor commented, "
Toni Childs backed by a rock band playing
Bobbie McFerrin's "
Don't Worry, Be Happy" comes closest as a description." Alan Jones from
Music Week felt it is "charming" and "easily the best track" of the album.
Steven Wells from
NME named it Single of the Week, writing, "This has a nine-foot tall titanium hook and a woman singer who does a fair bit of that
Bjorkish
OOOOOOEEEEEOOOEEE and seems to be demanding a revolution and is extremely pissed off about the world. Ooh, she's really getting going now. Damn, but this is good." R.S. Murthi from
New Straits Times called it "anthemic" and remarked that it "is probably one of the simplest and catchiest pop songs to be produced in recent times." Carmen von Rohr from
Rome News-Tribune noted "the amazingly down-to earth common sense lyrics" of "What's Up?", and added that Linda Perry "sings in her rich, soulful voice about the frustrations she feels as she tries to adjust to her place in the universe." A reviewer from
Sunday Life wrote that the song is "naggingly memorable". Ronny Johansen from
Troms Folkeblad commented, "What a wonderful use of voice and what an irresistible song!" Conversely, songwriters
Carl Barât and
Stuart Braithwaite named the song
the worst ever. Musician
Dean Ween said: "It's as bad as music gets... Everything about the song is so awful that if I sat down and tried to write the worst song ever, I couldn't even make it 10 percent of the reality of how awful that song is." ==Commercial performance==