Why is it a waste of time? It is exactly what it says on the cover, it’s a ferry from Liverpool to Birkenhead, were you disappointed because the cinema/pool/duty free shops were closed?
It’s a short boat ride that gives you a different view of the city and the area, it’s not going to rock your world, but then it doesn’t claim to.
It’s a great little city and there is plenty to do as others have said, Albert Dock, Cathedrals, the area around Wood St/Fleet St has lots of food places.