1. Despite both having "tabs on top", in Chrome tabs extend all the way to the edge of the screen. In Opera, there's a small unclickable border area. This is a basic, basic Fitts' Law mistake that makes it so much harder to click tabs.
2. Chrome does that thing where when you close a tab, the "close" button of the next tab ends up exactly under your mouse pointer. This is such a nice and natural feature that you forget there was any alternative. Firefox and Opera both get this so wrong.