The Hop On Hop Off bus and River Cruise are a good way to get a big picture view of some of the main sites and attractions. We only bought a one-day pass, using it to do a drive-by for some of the locations were knew we didn't have time to visit thoroughly, and to get the lay of the land, as it were. It was a good way to see a lot. We had already been in Paris for about five days when we did the Hop On Hop Off, so it provided a welcome respite for our feet, while we still took in a lot of sites, at least superficially.
We found the Paris Metro easy to navigate and used it to get back to the places we wanted to visit and spend time. I'm not convinced that the expense of a 2, 3, or 4-day pass would be worth it since the buses sit in traffic, just like all the other vehicles.
The river cruise is just an hour, but provides a very different and beautiful perspective on many of the buildings along the Seine. We were glad we did this.
The Skip the Line Eiffel Tower ticket name is deceptive. You don't have to stand in line to buy tickets to visit the Eiffel Tower, but you do have to plan your day around the time you are schedule to actually go up in the Tower, and you WILL, most definitely, STAND IN A LINE to get into the Tower, STAND IN A LINE to get into the FIRST elevator and then, if you decide to go to the TOP of the Tower, to buy an additional 6 euro ticket for the top of the Tower, you WILL STAND IN ANOTHER LINE for THAT elevator, as well as STAND IN LINES FOR BOTH DESCENDING ELEVATORS.
If you visit the EIFFEL TOWER, you will stand in quite a few lines unless you simply view it from Terra Firma.
All said, we thought it was worth it, but we were not visiting during a peak tourist time, so the crowds were not too bad. The view from the top of the Tower is unbeatable and to me, worth the lines, and the wait.