The first difference that I noticed is not only the text size (which is VERY different – especially the aspect ratios, compare the letter ‘o’ in the above examples), but much more impotant – the different line spacing. When measured in units of character height (which is how the human sight grasps it), the two examples are very different – which has a huge effect on how comfortable you feel with the text.

By the way, I consider myself the “average user”, for this matter.