His greatest achievement was by accident leading Britain out of the EU. It will save Great Britain in the coming decades.
Regarding the appointment of Boris, a very good move by May. As the Spectator notes...
Giving Boris Johnson the role of Foreign Secretary is probably the smartest single move that Theresa May will make in tonight’s reshuffle. It could well turn out to be one of the most important jobs in the Brexit era – a job of selling Britain to the world. A job that means explaining what George Osborne could not: that the Brexit vote was the act of a self-confident nation keen to make to friends and strike new alliances. That Brexit was not the sign of a Little England but of a country that has had enough of a Little Europe and wanted to lift its sights to more distant horizons. My biggest single concern of the May era is that Brexit might be interpreted by its opponents who saw it as vaguely xenophobic, or the sign of a nation looking in on itself. May’s holding line – 'Brexit means Brexit' – suggests even she hadn’t worked out how to describe Brexit. But Boris, as Foreign Secretary, will be the person who explains Britain to the world: a job that has been revitalised by act of Brexit.
His first task will be root-and-branch reform of the Foreign Office itself: too many diplomats saw Brexit as a disaster, and could not bring themselves to convey the message that this was the greatest-ever vote of confidence in the project of the United Kingdom; that Britain was too globally-minded to fit in the constraints of an EU that seemed to regard its mission as erecting a wall around Europe. Brexit should mean a revitalised Foreign Office, suddenly rediscovering the trade negotiating skills that it lost in the 1970s. What the Foreign Office needs more than anything else is an injection of optimism. And I can’t think of anyone better placed to deliver that injection than Boris Johnson.