(Original post by Paddington Bear)
Hey - usually I find it's best to approach a 'how successful' essay by working out the person's aims were in the first place, and then comparing them against what actually happened.
It's a while since I studied this period, but I guess I can share some thoughts on where to begin...
1. Church governance.
Was the Royal Supremacy successfully reestablished and a clear break from Rome made? Did Elizabeth manage to preserve the institution of bishops overseeing the Church (episcopacy) rather than a presbyterian structure of elected local 'elders'?
2. Doctrine and rituals - via media
or middle way in religious practice between Catholic traditions and radical Protestantism, preserving many old practices that give the impression of continuity with the past and resisting Puritan demands for further change.
Many Protestants would have argued that the 1559 settlement was temporary - the Church was "but halfly reformed". By refusing further changes (e.g. abolishing saints' days, wedding rings, bowing and kneeling at the eucharist, priests' vestments), did Elizabeth and her government betray the principles of Protestant reformation? Or was via media
a principle in itself?
3. Uniformity and enforcement.
What did Elizabeth want? Did she aim to force everybody to attend official communion services? Look mainly at recusancy but also perhaps at the Separatist movement or simply at how much her reforms were carried out and enforced. Did she turn a blind eye to Catholic recusancy or punish it too lightly? Was this intentional - did she want everybody to attend church and worship in the same way, or was she more concerned to avoid trouble?
4. Continued 'mainstream' Reformation.
Did English bibles continue to be printed, distributed and read? Were church services conducted entirely in English across the country for the first time ever? Did propaganda such as Foxe's Acts and Monuments encourage a hatred of the papacy? Did belief in purgatory, the cult of saints, pilgrimages and so on, disappear? (Yes, yes, yes and yes.) Did the vast majority of the population consider itself Protestant by 1603? (Yes - arguably the patriotic war against Catholic Spain in the 1580s helped cement this in the popular feeling.)
However, did she encourage preaching? (More doubtful - see, for example, the controversy with Edmund Grindal over 'prophesyings'.)
Just a few ideas but I hope they help :-). Make sure you cover a broad period of her reign rather than just 1559-63, and, again, be clear on what you consider the 'principles' of the settlement - or indeed whether you think there were any consistent principles.