$18/month? If I got all content that was produced for the entire history of the BBC, and all future content, then yes. I'm tired of having to wait for new episodes of QI to show up on youtube.
But keep in mind that content production is a fixed cost, so if you increase the number of subscribers you can lower the cost per subscriber.
You don't quite get everything-ever. Certain programs (including films) are made available online on iPlayer for a few weeks, but after that you usually have to wait for it to be repeated on TV (and usually again on iPlayer).
But keep in mind that content production is a fixed cost, so if you increase the number of subscribers you can lower the cost per subscriber.