The Eiffel Tower is among the world's most famous structures. By all means, go see it. Take pictures of it. Tell your friends you stood at the base and looked up into the tower itself.
But don't kill large periods of time waiting in line for the ride to the top. Eiffel Tower ticket prices for the top are €14 ($17.75 USD) for adults, €12.50 ($15.80) for ages 12-24 and €9.50 ($12) for ages 4-11 (under age four ride free). If you're willing to walk to the second level, these prices are more than cut in half. Note that you cannot walk to the very top observation level.
For those taking the elevator, this is a one-time experience you're likely to remember. When viewed that way, the costs aren't excessively high. But the investment in time you will make waiting in line for those elevators could kill a significant part of your day, depending upon the time of year.
It's worth deciding before arrival whether or not you want to make this investment. If you simply want a great view of Paris, there is a much cheaper way to go. Click "next" and see it.