There have been some reports in Japan concerning falling sales for the weekly manga magazines, with interviews with long-time readers who say they think the quality has dropped, causing them to lose interest in the publications. What with the time lag in local trends crossing oceans, maybe a decline in manga popularity in the rest of the world is in the pipeline. I'm no expert in manga and anime, but from what I've personally seen, I would tend to agree that a lot of the new stuff isn't as interesting as many of the older series were/are. Over the years, I've really enjoyed reading some manga series (in Japanese in order to learn Japanese), but I haven't found much that I'm interested in lately.
Aside from quality, I think manga has reached a saturation point in Japan. I remember about 15-18 years ago, when historical manga books were becoming popular, there were some concerned voices over the young people who were learning shallow history from easy-to-read manga and not reading proper books that presented history in any depth. History is never completely understood by anyone, and nearly always greatly misunderstood by everyone, but even so, worry over that shallow way of learning history may have been valid - many current twenty-something people (they don't quite know it yet, but they will-not & can-not stay there!) don't seem to be very knowledgeable about the basic facts of even fairly recent history).
For a while, it seemed like there were manga everywhere in Japan, and then manga began to be popular outside of Japan. Just about the time it was looking like there was no end to the growth in popularity of Japanesee manga, I think they have become a bit of a standard production thing, and creativity seems to be lagging. One exception seems to be "One Piece" which has some pretty creative story lines and has been (and continues to be) very popular, although the newest episodes of the animated version of that have become really bad - I don't know why that is exactly - one theory being that they had some catching up to do initially when the anime kicked in later than the manga, but now they're caught up, there isn't enough original manga material to fill up a 30-minute animation, so they put in meaningless filler in order to bring the show up to 30 minutes (with many commercials and a long intro and exit, more like 15 minutes actually). Whatever the reason, many of the latest animated versions of One Piece aren't worth watching).
One type of manga that seems to be selling well, are manga-novels, which people are reading at home I suppose - as you don't see much of them on the trains... which brings up another reason for the decline of the weekly manga magazines - cell phones! Before cell phones took over people's lives (text-messaging & games), magazines of all types were popularly bought from train station newstands to pass the time in the train reading. These days, when people aren't text messaging with their cell phones on the train (which they nearly always are - especially the early-twenties crowd, who I swear must be doing it even when they sleep), or sleeping (for the lucky few who get seats), I've seen more A-6 text-only paperback books in hand lately than comic books. The advantage of a text-only A6 paperback book, is that it's thin enough to easily fit into a pocket or bag, so they can be carried for a week or two or three. The small phone book sized thick magazines used to be bought for a single journey's worth of reading (usually on the homeward-bound evening trains), and then tossed up onto the overhead racks before getting off the train (to be picked up by someone else to read), but I hardly ever see that any more. (Since we entered the Age of Unknown Danger, railways have asked people not to leave things on the overhead racks like that, but I don't see many people reading them in the first place anyway.)
Lyle (Hiroshi) Saxon