Personally to me, osu! is something unique because it's not known by many people. Since it's popular, I lost the feel of uniqueness from osu! Why would the game be unique to me? It's because it was something I could show a friend at school, and get others interested because not many knew what it was.
Let's say for example, you have a favorite band that's not very well known, but in a few years it becomes surprisingly popular and nearly everyone you meet knows about it. To a person who's known about it before the boost of major popularity, it was something cool they could of shared around, but now that everyone knows who that band is, it feels uneasy to talk about it.
Of course, not everyone feels like that, but that's how I feel about it. I love osu! and I was introduced to it by a friend. As painful as it is to me that everyone I might talk to tomorrow will know about it before I could even explain to them about it, we'll just have hope for the best of osu! Yeah it's great that osu! will get a bigger fanbase, everything comes with the good and bad outcomes.
Again, this is my opinion, there are many other reasons why people agree or disagree with Pewdiepie's decision to play the game. Just remember, just because you played doesn't mean he can't (Just like pewd fans telling other youtubers that they can't play it
) It was very painful to watch him play, but it don't matter, we can still enjoy it whether there's pewd fans or not.
Although, DMCA copyrights... here they come......