138 minutes of slaps in the face to the expectations of spectators, whatever category they belong to, especially those who could see Joker as a revenge, albeit in a criminal way, of the loser, or worse as a sort of dark version of the V of V for Vendetta, an anarchic force fighting the system. 
In the end, the Joker is still him, Arthur Fleck: a loser, and his story is not a superomistic apotheosis, even in the worst sense of the term, but a self-destructive parable: the only difference between the Arthur Fleck before and after Joker is that the loser at the mercy of the system has become a loser at the mercy of the system, of his own madness, of his own fame and of his own admirers (whether fame-seekers or potential terrorists) and their expectations.  A monster that breeds monsters, who in turn sabotage his every chance at redemption, whether by tickling his worst instincts - the ones that made him lose touch with reality - or by physically interfering with his punishment.
Play with the spectator's expectations, the director, taking a pickaxe at all the narrative schemes he uses in the film, starting from the musical (an alienating way of showing the protagonists' thoughts and their detachment from the real world at the same time) to the typical narrative motifs of the procedural drama. By entrusting everything on the shoulders of Joaquim Phoenix, who, as we know, are strong enough to withstand anything, Phillips allows himself a staid and (perhaps a little too much?) free direction which conveys the tone of the film well and allows the spectator to never get distracted from the flow of the story.
Is it inferior to the first? But of course, (almost) every sequel is, what news. But it is an excellent sequel, which has the rare merit if not of adding something to the original, at least of better contextualising the story of the first film, instead of simply repeating it.
If you are looking for a comic book film, this is obviously the one wrong movie. But if you ask me, not even the first film was a comic book.