Seriously, Bush in using a major speech at West Point to articulate a "pre-emptive" US foreign policy basically suggested to our allies that the US reserved the right to launch a war against any other country on our own initiative, so long as we thought US long-term security interests required this.
This "pre-emptive" war doctrine somewhat resembled the one that Israel has maintained for many years, and most people don't like it much when Israel attacks her neighbors without any clear provocation, either.
But Israel despite her nuclear arsenal and her great Air Force is still a small nation, and Bush was announcing a "pre-emptive" war doctrine on the part of the world's greatest military superpower.
Bush's policy was therefore perceived by many people around the world -- including some who didn't like Saddam Hussein -- as being extremely aggressive, arrogant and dangerous.
Bush also did many things in foreign policy unilaterally - without first consulting US allies, or doing them despite the disapproval or our allies. Naturally, that led many Europeans to despise Bush.
http://en.wikipedia.org/wiki/Bush_Doctrine
Obama's willingness to launch air strikes against Libya shows that he's hardly a shrinking violet in foreign affairs. But he's not perceived as being the swaggering, arrogant American bully -- the loud-mouthed, drunken American cowboy -- that Bush was perceived as being. And so he's liked much better.
To be fair to Obama's critics, the current president is something of a "contrast gainer" when seen against Bush. That is, Obama gains a lot by contrast, gains by simply not being George W. Bush. If the Europeans hadn't hated Bush quite so much, they might not like Obama quite so well.