I liked their early stuff

Standard response from someone who either is "in the know" or someone who thinks they're in the know about a given band, tv show, author or any other collaborative artistic effort that has either gone bad or gone mainstream/sold out.

This is always subjective.

Sometimes you hear this from someone with a genuine complaint, but more frequently it's a setup for a pretentious rant about how so and so sold out to the man, gave up the ghost or got interested in making money more than art.

Targets of this sort of criticism are endless - but especially centered at bands and the like who started out as relative nobodys and ended up big name superstars. Nirvana is a common example, but I even heard this about Radiohead the other day... so you never know.

An interesting variant on this, and one I am occasionally guilty of myself, happens when a band with a long career has a period of commercial failure after their success - this is particularly true of bands from the '60s.
"The Beach Boys? Don't like the early stuff - Surfin' USA, Little Deuce Coupe... Far prefer Friends or The Beach Boys Love You. You've never heard of them? Shame..."
"The Kinks? Don't like all that You Really Got Me, All Day And All Of The Night stuff... I prefer the later stuff - The Kinks Are The Village Green Preservation Society, Arthur, Or The Decline And Fall Of The British Empire - you know, the good stuff..."