It's not about one feature; it's the completeness of the whole browser. Things that you'd expect in Firefox/Chrome in extensions are built in here. It's still as fast as Chrome to the user, never mind silly benchmarks. Give it a spin some time.
Another thing that makes me stick to it is the integrated mail client. It's extremely minimal, out of the way if you don't need it. My browser is always open, so having a built in client, that indexes my email, and is searchable even if i'm offline is definitely awesome. I don't need to use Thunderbird, etc, since the minimal features are all i need. Give it a spin!
Tabs cannot be dragged in and out of windows
Text cannot be selected and dragged into the URL bar
I also fell in love with tab stacking. It's just easier to group tabs into stacks in a single browser window than having separate windows. In later case I spend waaay too much time clicking wrong window.
You can right click the text and select "Go to web address". It's quicker in my opinion.