For years failblog.org was basically one of the best online blogs in existence. Its major shtick was to publish (at least daily, often even several times a day) images and videos, sometimes other forms of media, of people or things failing in some manner (usually hurting themselves in the process, although that was certainly not the only type of failures), such as for example skateboarders failing a jump and faceplanting, boats getting destroyed by a crane accidentally failing and dropping it, and so on and so forth. (The blog has a strict policy that they will only publish fails that remain at some level of good taste. No people getting killed or seriously injured for life, for example, and no gore. Emphasis on humor, not on morbid curiosity.)
It remained like that for a rather long time, and I was a very avid follower.
Then at some point it started to change. While failblog has always published other kinds of things (mostly related to internet memes) from time to time, it was quite rare, and they mostly concentrated on actual fails. However, at some point they started publishing more and more material unrelated to fails and more related to whatever internet meme was popular at the moment.
For a time it was still not all that bothersome because the quantity of actual fails was still pretty high. However, as time passed failblog.org basically turned into a blog of internet memes. The amount of actual fails plummeted to almost nonexistent. For example, last time I checked it, something like one entry out of twenty was what could be considered an actual fail (even by the loosest definition) while the rest were completely unrelated. (If counting in a stricter manner only the type of fails that they used to publish in the past, the number is even smaller.)
I struggled with it for several months, perhaps even almost a year, but at some point I got completely tired and stopped following the blog altogether. It was outright boring, and wading through the hundreds and hundreds of entries to see the half dozen of actual fails was a pain. It made no sense.
They should really rename it to "memeblog.org" or something similar, because the name has become a complete misnomer. It's a real shame because it was one of the greatest blogs in existence, but now it just sucks.
Of course failblog is not the only online medium that has suffered from this. Many blogs seem to go through this, but also other types of websites, such as webcomics.
One of the most infamous and known ones is probably MegaTokyo. When it started, it was a light-hearted, humorous, "animesque" (well, "mangaesque" would be more accurate) webcomic that was fun to read and follow. It remained like that for several hundreds of issues. Then it slowly but steadily changed.
There was apparently more reasons for this change than just the authors shifting genre, as it seems that one of the two authors got into a dispute with the other about the content and leaving. Anyways, regardless of what the actual reason was for the changes, they were for the worse. While the quality of the artwork became significantly better and more detailed over time, the same cannot be said of the storytelling. Ok, the storytelling became more detailed, but it did certainly not become better, but the exact opposite. The storytelling slowly became complex, intricate, quite hard to follow and outright boring. It was also paced and depicted in a manner that made it even harder to follow, jumping all over the place with no well-defined structure. Only rarely was there any humor left, and the vast majority was just a complicated mess.
It doesn't help that the author seems incapable of establishing characters properly, in a manner that readers will easily remember and recognize them. There are tons and tons of characters, but it's very hard to remember who is who, what that character's role was in the overall story, and why he/she is doing whatever he/she is doing at the moment. It doesn't help either that many characters look very similar and thus are easily confused with each other. (This is very much unlike what the comic was at its beginning, when there were just a few characters that were very easily recognizable and easy to remember.)
This is, of course, not the only webcomic that I have stopped following. I used to read Least I Could Do, but I haven't been following it for years. (It went through several instances of complete art shift, due to changing artists, but that's not the reason. The reason is that it just became boring, repetitive and lacking of fresh ideas and content.)
One of the webcomics that are still widely regarded as one of the best, but which I stopped following out of pure boredom, is Penny Arcade. The same story repeats itself: For years it used to be smart, witty and funny, poking fun on video games and related stuff. Then it slowly started being more and more obscure, less and less funny, the actually funny strips becoming rarer and rarer... At worst I could shift through about 50 issues and find maybe 2 that were actually funny. I just stopped following it.