If you want spec comparison, go here http://geekaphone.com
I like the nexus over the s2 because of a few U.I features and the curve design. And with the new upgrade for the nexus OS, one of the features that I liked in s2, the slide writing; will be made available along with a better, far more complex panorama (3D) photo capturing ability. So all in all, nexus is a better buy over an s2, but I don't think the volume feature would improve with the OS upgrade, though.