I think this comment from an earlier thread explains it well. I'd credit it, but the guy deleted his account.

It's innovative, but obsolete. I think most of the acclaim comes from it being "good" back in the day and so students/professors/critics perpetuatd that belief despite it becoming more and more incongruous with what we expect in film today. In other words, I think most people who saw it today who DIDN'T know about its legacy would think it's okay at best and awful at worst.

This academic "bullying" of some sort tends to make anybody who takes film seriously but doesn't like CK feel like an idiot or a philistine or that they're the ones that need to explain why they don't like the film (i.e., shifting the burden of proof). I'm much more outspoken about it, but I feel sorry those who aren't or are forced to assimilate and write essays about why it's so great despite not liking it themselves.

This coupled with the fact that so many people, IMO, are sucked into the hype creates a plethora of analyses that make the film seem more complicated than it really is... in other words, any film with that many followers is going to accrue an insane amount of arguments in its favor... the same reason why if you go check out the wikipedia page of a popular hip-hop song, you'll find an overly wrought description of the song structure (despite the fact, that most of those songs use about 3 chords and are written in 4/4) even though more complicated, but less popular songs, tend to lack these kinds of analyses.

Hype aside, the acting is stilted, the themes aren't very thorough and like an M. Night Sham film, the merit of the film is almost entirely based upon the twist (i.e., plot driven as opposed to theme-driven). What you're left with are generic platitudes that are hardly explored (e.g., "Money can't buy you happiness," "Power corrupts," etc.) and just plain boring to anybody who is being honest about it.

As for the mise en scene, again, innovative at the time, but completely overshadowed in the decades to come.... and I'm not just comparing it to modern film either... even films created by the late 50's and early 60's make CK's photography look dull.

To be fair, this phenomenon isn't exclusive to CK; it's true of other films as well (e.g., Bicycle Thieves) and other mediums in general. I think if people are looking to find intelligent, classic films that are still relevant today, they can do much better than this film and others like it.