Not because the imagery is really all that shocking. At over forty years remove, the "shock" of the tittalating visual sexuality of that future (technically now an "alternate past") has been drained of most of it's energy. In fact, it's rather amusing and quaint, and oh so very "the future of 1970" in feel. And the portrayals of "ultra-violence" likewise. Alex and his "droogs" would have been chewed up as a light snack by any real-world contemporary urban street gang.
I think that's what makes it hard to watch, is that I can see what Kubrick and Burgess were trying to do, and they were being rather dumb about it. They were being so in the way that most every other non-genre writer is when they try to slum around in the SF genre neighborhood. Heck, SF writers from the mortifying era of Hugo Gernsback often did a better job of thinking their way thru the social implications of social and technological changes, and by the time that John Campbell was at the helm, quite a lot better.
Piers Anthony once wrote a schlocky SF novel titled The Ring, and everything that A Clockwork Orange was about, The Ring did better. (Otherwise, Anthony's novel was
Hell, Anthony even got correct the need for protective oversight of "the cured", and the deep social divide between "normal people" and "the cured", that the people in ACO were so surprised to discover and exploit.
This movie is important because of all the cultural referants based on it.
But as a story of ideas, it doesn't live up to the hype, and the older it gets, the less it does.