I didn't see the series from the start but what has been interesting for me:
Bea vs Kenneth, Tom and Freddie
Marcus vs Bea
Bea's realisation that not everyone saw her as she did when they all couldn't stop laughing.
For me I think the problem is that one sole housemate isnt all that interesting but rather how housemates interact with one another. Therefor it is bound to become a lot less interesting at this point for me.
If they have more controversial housemates in I think folk will find it even harder to relate to them (which for some seems important). If they don't it may be seen as too boring. Because of this I think Big Brother has intrinsically a limited lifespan.
Ofcourse that could all be rubbish and it will just continue along with a die hard fan base. It still does seem to be able to get quite a lot of people emotionally involved though perhaps more negatively now then before?