(Disclaimer: I don't know every manga ever made, so I may be totally wrong about any of these, but these are the trends I've observed in some manga/anime that's popular over here.)
OK? OK. Let's go.
Character Development: There Isn't Any
|Pictured: The only expression this character ever has.|
Yes, this is far from a universal rule. Older series like Gundam Wing or Ghost in the Shell or Akira feature more complex, nuanced characters then we see today. Apparently there was some arbitrary dividing line sometime in the ‘90s that decreed all characters from then on should suck. Shows like Death Note or FMA tend to avoid this trap, with complex lead and even subsidiary characters, but look at a show like Bleach or One Piece or Naruto or Dragonball Z. The main characters are utterly uninteresting, and invariably share a strong desire to protect those closest to them. Well, no shit.
Moreover, they never really change! Goku is still the same happy-go-lucky goofball at the end of DBZ that he was at the start. Ichigo is the same tough-minded-but-good idiot in Season 14 as he was in 1. Naruto wants respect, he wants to be the best, and (surprise) he wants to protect his friends at the start and at now. Nothing ever changes, hobo!
Why It's Bad: Who wants to read about an unchanging brick for 50 volumes? I mean, apparently people do, but why?
The Ages of the Main Characters
|This kid was turned out of his home at age 12 and sent to live in a world full of monsters and criminals.|
I get that the authors are writing for a specific audience, but still, isn’t it a little weird that almost every major protagonist in the known manga universe is between 11 and 18? Ash Ketchum begins his series at 12. Ichigo is 14 or 15. Luffy is 17. Light Yagami is 18, although he does enter college after three volumes (Death Note is an outlier in a lot of ways). Edward and Alphonse Elric are something like 15 and 12, respectively. Yusuke of Yu Yu Hakusho is a junior high school student.
Why It’s Bad: I mean, it’s good for that age group, you know? But it’s hard to relate to these characters as a third-year college student. Where's the manga/anime that deal with more adult issues? (It’s entirely possible they’re out there, I just haven’t heard of them.) And why are the stupendously popular ones all about teenagers?
This leads us directly into the next problem, which is…
Romance (Doesn't Exist)
Ichigo and Orihime/Rukia. Edward Elric and Winry. Rurouni Kenshin and Kaoru. Ash and Misty. Naruto and Hinata, Kusanagi and Batou, Heero and Relena, Zecks and Noin, Riza and the Colonel, Sakura and Sasuke.
What do all these couples have in common? They never bloody get together during the run of the show. Sometimes, they will go for a dozen seasons, or even the entire run of a show, without ever acknowledging that they have feelings for one another, never mind (heaven forbid) going out on a date or anything. Other times, they will get together in the end (Kenshin and Kaoru, for one) but it'll take ungodly long for it to do so, and there'll be all sorts of contrived reasons holding it up. It's like every animanga used Bones as its romantic model.
There are a few exceptions to this rule-Son Goku and his wife, Light and Misa-but those relationships go largely ignored in the greater series. Goku's wife isn't memorable enough for me to even remember her name, and Light has no affection for either Misa or Takada, preferring to use them to further his plans. In other words, theirs isn't a big romantic relationship where the romance is plot-important.
Why It's Bad: For the same reason it’s bad to watch an unchanging Easter Island statue in the place of a main character: after a certain period, don’t we just get bored of these characters “liking” one another from a distance? I sure as hell do.
Characters Can Just Be Idiots
I’ve never seen another art form that as frequently writes in its characters as total morons. Whether it’s running around and screaming at the slightest provocation, a total inability to grasp what’s going on in the plot, or the inability to adapt to new circumstances when they change, almost every anime falls into this trap. Usually this isn’t a huge problem for the main characters, but One Piece, Fullmetal Alchemist (anime) and Bleach all have a bad habit of writing in subsidiary characters whose only function is to run around and scream that the world is ending. Why do these guys (they’re generally male) exist?
Granted, this is by no means universal, and in some series (Death Note) the characters’ special abilities are being incredibly smart. But even Death Note has its Matsuda. And every anime series (and most manga) has those godawful sequences where the animation goes to shit, a goofy background pops into view, and the characters run around like idiots crying hugely exaggerated tears and screaming their little heads off. What could possibly be more annoying.
Why It's Bad: Look at this picture. LOOK AT IT.
Those Goddamned Filler Episodes (And Arcs)
Filler episodes typically happen when a manga/anime franchise becomes schizophrenic. Often, the franchise will start out as a manga drawn by an individual artist (with maybe a few helpers), and then get picked up for an anime run that may go in a completely different direction then the original manga. (See: Fullmetal Alchemist, and to a lesser extent, Death Note). However, when the anime follows the manga more or less exactly (as in Bleach), what frequently happens is that the anime is easier to do and will catch up with the manga faster then the artist can draw the new panels. When that happens, the entire series can get stuck in a miserable filler arc that intentionally has no relevance to the ‘main’ arc (think Kiefer Sutherland of 24 randomly spending a day fighting terrorists in Chechnya), which has no connection to the original artist, giving the artist time to draw new panels.
Why It's Bad: The filler episodes are unadulterated crap. The filler arcs waste the time of the producers and the viewers. What’s wrong with taking a few months’ break, or showing reruns for awhile, so the artist can catch their breath?
The whole thing is partially because of the rather ruthless exploitation of animanga franchises in Japan. Take Bleach, for example. the nine-year series has spawned 48 book collections, 14 anime seasons (in less than ten years!) collected in 49 DVD sets, eleven soundtrack CDs, four feature films, seven rock musicals, two trading card games, at least four video games and fuck all knows what else. Look it up on Wikipedia if you’re interested.