Vlc is one of the top most used video player Software, I think this is because it supports most video file types and also because it is very easy to use. It is still one of the best out there.
Another important issue is that it is always updated, there are always reviews about the software. Discussions and views of some of their developers and programmers are published.
Finally I would say it is being sustained financially, because in my research I found out that they have lot of partners that support their project.
My three points:
1. It is widely used
2. It is updated and there always new releases
3. They are sustained financially
I think these three points are very important for an Open Source Software as they shows that the project is being very successful