Most of the negative reviews here criticise this movie as being dated and for idolising the waster culture - possibly related criticisms - but it's difficult to see how you could justify either except on a very cursory consideration of the film.
Easy Rider absolutely refuses to idolise the sixties ideal, and it is not to my eyes even vaguely dated (I say this having seen it for the first time last night, thirty three years late).
The golden thread running through this film is that THE PARTY'S OVER, DUDES.
Fonda states this explicitly ("we blew it...") and it's firmly implied in a devastatingly funny caricature of a dead beat hippy commune (as the city dropouts joyously commune with nature, scattering their seed on the barren land of the New Mexico desert, Fonda asks wryly, "do you, ah, get much rain up here?")
And (without wishing to spoil the ending) by the time the credits roll, our heroes haven't exactly profited from their wild lives. The ending of the film is profoundly pessimistic about the prospects for freedom and independence.
The film is certainly critical of the intolerant "establishment" (which nevertheless prevails), but if there is one character who does smell of roses, it is the farmer who takes the boys in for the night and who, says Fonda, should be proud simply for living off the land.
For my money this makes Easy Rider ahead, rather than behind its times. It's also rooted in a number of great cinematic traditions, aside from the Road Movie genre which it helped to invent. I like the idea (expressed in a review below) that this is a latter day western, even down to the character's names, Wyatt and Billy. Also, were you to draw a line between Butch Cassidy & The Sundance Kid and Thelma & Louise, it would intersect Easy Rider.
The performances of the cast are delightful - Nicholson's is rightly feted, and Hopper's is very Dennis Hopper - fans of Apocalypse Now will recognise this style in which Hopper doesn't really act so much as simply looning around - here in total contrast to Fonda's studied coolness, which holds the film together, reinforced with a cracking soundtrack (in this regard also, Easy Rider was well ahead of its time).
If you fancy a dash of counterpoint, try watching Easy Rider back to back with David Lynch's stunning recent work The Straight Story - as a compare and contrast job, I think they'd make a fascinating study.