From The JRR Tolkien Companion and Guide by C Scull & WG Hammond, page 251:
"Tolkien's antagonism to France, the French and the French language was due, in large part, to his regret that English culture was dislocated and nearly destroyed following the conquest of England by French-speaking Normans in 1066."
I feel pretty much the same about 1066 as does Tolkien - the worst of the axe blows at the spiritual roots of England.
Probably the second worst was the Dissolution of the Monasteries under Henry XIII - I didn't really appreciate the gravity of this until I reas EK Chambers (http://en.wikipedia.org/wiki/E._K._Chambers) biography of Thomas More.
(And this was a book I read about in the above cited Tolkien Companion and Guide - Chambers was a friend of Tolkien's, and a fellow Roman Catholic).
The Cromwell revolution was another axe blow to England's spirit; and the 1914-18 and 1939-45 world wars were two more - mainly because of the huge kill-off and destruction of the cream of young men (especially in the 14-18 war).
I watched the first episode of a recent BBC TV programme about the Normans, which programme was very well done, but which I found almost painful to contemplate.
My conclusion? The Normans'... (ahem)... efficiency, was certainly very impressive. They were great (and fortunate) conquerers and highly effective at ruling.
And on the aesthetic side, they built my favourite building in the world - Durham cathedral.
And yet, and yet...