Quirky, dated, yet very influential for its time
Can a film be both influential and dated at the same time? This film is proof that it can. I can understand how the film's quirkiness makes it not for everyone. A lot of people complain about the shrill electronic sound effects. The portrayal of homosexuality and the state of the art technology make it a somewhat dated film.
However, one has to take in consideration the time in which it was made, very much a time of a transition. Note the portrayal of the Mafia, in particular the scene with the old Mafia boss Papa Angelo sitting at the lake, and remember that this was made before The Godfather and the gangster films of Scorsese. The actor who played Papa Angelo (the other wise unknown Frank Macetta) had an uncredited role in the Godfather, an obvious nod by Coppola.
Then there's the illegal audio surveillance, pre-dating both Watergate and Coppola's The Conversation. This has been touched on on other threads, so I won't need expand on that.
What's more, the scene in which the gang tries to get the code for the art collector's safe seems to have influenced A Clockwork Orange. The combination of the gang's masks, the colour schemes in that apartment, the smashing of sculptures and the harassment of the art collector's wife: these all seemed to have found their way into Kubrick's film in some form or other.