No play I have ever read - nor, I am told by those that know, that has ever been written - has the same complexity and scope as King Lear. The depth and intricacy of the plot and characterisation and above all the imagery which permeates the entire play is simply too big to 'get'. You can never really get hold of King Lear like you can Romeo and Juliet or MacBeth or even Hamlet: it is enormous.
Discussing it on E2, then, may seem like a pointless exercise. You need to write a damn book on it just to get started. Still, it may be useful to outline a few of the key ideas which can help to get some sort of grip on this unwieldy beast:
The overarching imagery and themes are associated with nature. The word 'natural' crops up at least 40 times in the text. This is what the play is most fundamentally about. Two versions of nature are presented. There is that of Gonerill, Regan and Edmond, which is brutal, uncivilised and base - for them, to be natural means to be entirely selfish, literally animalistic; and that of Cordelia, Kent, Edgar, and, ultimately, Lear himself, which is about natural love and 'filial bonds' and harmony and perfect order. Inevitably these two visions must clash: this is where the dramatic meat of the play comes from.
There are constant references to the natural and the unnatural throughout the play: look at one of the scenes noded by Fred Bloggs (the) and you will probably find one. This is a subject worth a thesis: if you want more on it I recommend John Danby's brilliant and accessible analysis Shakespeare's Doctrine of Nature.
Other major themes include sight and blindness and 'everything' and 'nothing', both of which largely refer to the moral and material states of the characters. Often these two values are diametrically opposed: as Lear descends into madness, he gains a kind of moral might lacking before, whereas Edmond loses all our sympathy as he gains in power and possessions because of his evil actions.
Some general tips for thinking about the play, all more or less verbatim from the mouth of my excellent teacher:
Consider when the characters are acting and when they are being themselves, or natural. This is particularly important on the heath, when, with Poor Tom/Edgar, the fool, and Lear, all three figures are playing some kind of role.
Consider how you react to the horrific scene of Gloucester's blinding, and also to the sick humour about 'eyes' which follows. Is it guilt or embarrassment, horror or fascination? Why does Shakespeare want to implicate us in the tragedy by making something funny and then making us feel ashamed for laughing?
Consider whether you would read the play differently if, as was originally the case, it was not called a tragedy but a Chronicle.
Consider the similarities between Cordelia and the Fool, in particularly in terms of their relationship with Lear.
Consider what the point of having a parallel lesser tragedy which has its climax 'off-stage' is. What is the effect of the Gloucester plot?
There is so much more that I'd like to discuss, but this will just become a book. I haven't even mentioned the end, which is the most interesting and debatable bit. I'm studying the damn play for A-level. how on earth do you write about King Lear in an hour and a half? How can that possibly be long enough?