I think it is a valid question to wonder if the Bush presidency was the worst ever. George W. Bush certainly had a whole list of failures -- from a failed economy going into recession (and costing millions of jobs) to two unnecessary and very expensive wars and a pitiful and inadequate response to Hurricane Katrina.
Bush still seems to believe that history will treat him kinder than the general public does (where a majority still consider his presidency to be a failure). But he may well be wrong about that. Siena College did a survey of historians in this country back in 2010 (the last time such a survey was done), and the verdict of today's historians was that President Bush was the fifth worst president this country has ever had. Only A. Johnson, Buchanan, Harding, and Pierce were seen as worse presidents than George W. Bush.
The historians rated each president in 20 separate categories. Bush was rated next to last in several categories -- foreign policy accomplishments, handling of U.S. economy, ability to compromise, and communication ability. Overall, they rated Bush 39th out of 43 presidents (with President Obama not being rated because his president was not yet finished).
The following charts are from the Washington Post's Wonkblog, and illuminate some of the Bush presidency failures. There are more charts and a discussion of them at that site, and it's worth a visit.
And if that's not enough for you, Alternet has compiled a list of 50 reasons why Bush was a poor president. It highlights the shockingly bad Bush presidency.