Much of what William introduced in England was not so far removed from what the Franks introduced in Gaul, but what he did do was reinforce his central rule with written laws. All land was turned over to the Crown and was granted or confiscated as a gift or punishment. He introduced a true form of feudalism and a raft of new laws designed to discourage revolt and force loyalty to the Crown and Norman landowners. Land was granted to the Church and a law introduced reinforcing one God and one religion so ensuring the future power and wealth of the Catholic Church.
The biggest changes he made were intended to increase Norman control over wealth and power and excluding the Anglo-Saxons. The Anglo-Saxon elite who had fought for Harold had their land confiscated and settled on Williams Norman followers. Land inheritance was controlled by forcing Norman marriages on all bereaved widows and daughters with a claim to property and land. High offices in the Church and Government were given to Normans, ousting almost all the native Anglo-Saxon holders. This meant that all Bishops and Barons and most Abbots and Sheriffs of the shires were Norman.
On a more positive note, he abolished execution, replacing it with blinding and castration, introduced trial by combat or by ordeal by hot iron and ended the trade in slavery. Well it was the Dark Ages after all.