Hi there!

I suppose I am wondering what differences you really have in mind. Off the top of my head, you might be referring to a distinctive visual style often associated with manga/anime? If so, that style is often traced back to the work of Osamu Tezuka (1928-1989), especially to his seminal children's manga Mighty Atom (more commonly known as Astro Boy). Here is an image of the title character as drawn by Tezuka that is fairly representative of Tezuka's overall visual style. Far and away the most striking feature of the design to modern fans of anime are the large, highly expressive eyes, a hallmark both of Tezuka's work and of much of the work that would follow in his wake in Japan. However, even this most emblematic of manga/anime visual tropes is not entirely without earlier precedent. Betty Boop is often mentioned as a probable influence (note the similarity between her eyes in the linked image and those of Astro Boy). This isn't to downplay the originality of Tezuka, who is an acknowledged giant not just of manga but, I would argue, of visual arts in the 20th century more generally. But we should always be cautious about drawing too firm a distinction between Japanese and Western comics/cartoons (and indeed cinema more generally: Satoshi Kon's imagery has shown up in the films of Chris Nolan, for example). Then as now, there was a lot of cross-pollination going on.

In terms of subject matter, I suppose I also see more similarities than differences. In terms of broad narrative thrust, how different are things like Dragon Ball Z or Sailor Moon from Western counterparts like, say, Thor or Wonder Woman? Aliens, superpowers, lots of action broken up by occasional slapstick, easy to understand morals, etc. I suppose there is a greater comfort, broadly speaking, with sexual content in Japanese works... one questions whether ChiChi's character design in early Dragon Ball would have passed muster in America in the late 1980's. The explicit lesbian relationship in Sailor Moon was also famously censored for American audiences. This speaks to cultural norms regarding sexuality and what is and is not appropriate for the young audiences at which these shows were primarily aimed.

Now, that is not to say that there isn't a lot of manga and anime aimed at non-kid audiences. Neon Genesis Evangelion is a landmark series in this regard, dealing as it did with issues of suicide, self-loathing, gender, explicit sexuality (perhaps most famously in the hospital scene in End of Evangelion), as well as themes and imagery drawn from sources as diverse as Freudian psychology and Christian spirituality. In many ways, this show proved that you could tackle "serious" material and still make absolutely mind-numbing amounts of money. I'm not sure shows like Revolutionary Girl Utena, with its focus on gender identity and sexuality, or even more recent fare like Erased, with its central focus on child abuse, exist or have the same level of impact/budget without Eva proving that such things could be profitable. So, despite all its flaws (and they are many), the current industry owes a lot to the influence of Eva. Another way this shows up is in terms of visual style: Try and count how many times you've seen a character who is clearly influenced by the iconic character design and personality of Rei Ayanami from Eva.

Now, all that said, it isn't as though this sort of thing is absent in Western comics. The works of Alan Moore are probably the best known examples (the bomb-throwing anarchism of V for Vendetta, the Juvenal and Shelley-quoting Watchmen, or the seminal re-imagining of the Joker in Batman: The Killing Joke). But there are also works like Maus by Art Spiegelman, a Pulitzer prize winning Holocaust narrative. Or consider the excellent (and less depressing) Logicomix, which takes for its subject matter the life and work of philosopher and logician Bertrand Russell (of Russell's paradox fame).

Sorry if this is more rambling than anything else; again, I wasn't precisely sure what difference you had in mind nor what exactly you were looking for in an answer.