Although a 'punk' in my early years, I have to agree Andy M that the music has not dated well, and was in many cases no more than 'Pub' rock. It certainly was more about expression and quickly became a cultural movement.
However it did rid us of ELP, Yes and the likes, but more importantly showed the youth of the time that being in a band was not elitist, but something anyone could do if they chose.
Of course many of the more noted bands of the movement, The Jam and The Clash for example, were never really 'punk' bands in the true sense and their music is imo a testament to the fact that there was some great music coming out of that era.