There's no 'do not track' option.
More options for cookies, like 'block 3rd party cookies'.
Being able to set the default search engine.
An ad blocker (like Mercury browser). I could live without this feature as I'm not optimistic about it being added!

These features are available in other browsers and their absence from Opera stop it from being my default browser. I love the new sync feature and would like to use Opera Mini more often than I do.