Seems to be Palatino Linotype (that's the first one of the font-family my OS has available). Not sure why Opera has decided to italicise it though, as the installed font looks fine normally.
Palatino being a pre-computer font also has a tendency to be hurt by screen aliasing a lot. If you can activate some sort of anti-aliasing/smooth font layer on your computer even the italicized version shouldn't look so painful.
