Deleuze's main project was a complete overthrow of what he termed 'the dogmatic image of thought'. By this I believe he meant to really overthrow the shadow of transcendental idealism and essentialism in philosophy: the notion that beyond appearances there are pure essences which somehow should govern the way in which we construct subjectivity and the manner in which we organize our values. In other words, an ethical question. It is , in one sense, an attack on idealism, in the sense that philosophy implies that there is some a priori, essential and constitutive quality to consciousness or 'being' that transcends or somehow precedes all the other faculties. He finds this fault in Kant, to a certain extent, and also in Hegel.
Deleuze believes that this is bad philosophy. It causes us to place all of our faith in an ineffable transcendent something that escapes mundane and lived experience. It suggests that lurking beneath the surface of appearances in life is some transcendent unity which is achievable through adequate purity of thought or action. It is as absurd as looking for the 'essence' of music by breaking open a radio. If we remain trapped within notions of transcendent essences and a priori causes, thought becomes a means of creating images that then torment us with our comparative imperfection. We are never the ideal, always the simulacra, a poor copy of some distant and perfected original. Deleuze completely refutes this idea, and the thought of any resolution of human being into transcendent unities or essences. There is no underlying unity that undergirds consciousness, in Deleuze. You can't break open consciousness and discover some sort of animating essence behind it. Instead he proposes something radically different.
Deleuze's critique of the dogmatic image of thought actually runs parallel in many ways to Foucault's critique of the 'Empirico-transcendental doublet'. Foucault's point in 'The Order of Things' was- to grossly oversimplify- that the transcendent ideal we see in representation and representational thought has become a tool for governance and ultimately oppression. We are indoctrinated into and strive for an ideal- often represented as a normative medical 'model'- which is often represented for us as an unattainable image. This produces extremely rigid regimes of reproduction and representation that get mistaken for social reality. We are told that representations and models are forms of ultimate truth, and that our own experiences are unreliable. The 'image' of thought thus becomes dogmatic. From this proceed overly restrictive moral codes, hierarchies and hegemonies of violence, fear and shame, unnecessary taboos, regimes of normativity and so on.
This includes, of course, the image of the transcendent judgmental God. Note that Deleuze and Guattari borrow the term 'body without organs' from Antonin Artaud, who said in his radio play 'To Be Done With The Judgment of God": When you have made him a body without organs, then you will have delivered him from all his automatic reactions
and restored him to his true freedom." So from the very start, I believe, Deleuze's project- how to teach people to build a body without organs- is a profoundly ethical one. He is showing a way toward constructing a new subjectivity, one that doesn't rely on essences or on transcendent ideals . A subjectivity that doesn't feel impelled to rigidly model itself on stale representations.
So what does Deleuzian subjectivity rely on? It relies on difference in itself. Difference in itself is really the key radical concept in Deleuze. Unfortunately, it is nearly impossible to understand unless you have some notion of the Bergsonian notion of time. For Bergson, the quality of a thing is not separate from its place in time: there is no way to separate them. This includes human subjectivity. Bergson's notion is that by abstracting human qualities we completely miss their actual pragmatic intent and functioning. Time is a component of becoming. Nothing comes into being without time elapsing. The one constant of time elapsing is that it perpetuates continuous change. So an acorn is never a static acorn, it is also, somewhere along its timeline, a sprout, a fully grown tree, a decaying log. So in this sense, an acorn differs-in-itself. It's latent potentiality of becoming, it's radical differentiation from its current form, is already present within it. It is already in the process of becoming what it is not. Human beings are exactly the same. We differ inherently from what we are ineluctably changing into.
Keep in mind, also, that Deleuze adopts Spinoza's completely immanent view of nature as one infinitely extended substance. Thus there is no transcendence in Deleuze. There are temporary hierarchies and strata of different intensities that come into being, but ultimately everything is coextensive with everything else. We might see 'everything' as a vast immanent folding and unfolding continuum, something that unfolds over time and allows 'difference-in-itself- to unleash itself into multiplicities of being. Difference in itself pushes matter into the animal which unfolds into the human which then unfolds into the supra-human. We are not discrete essences powered by transcendent hierarchies, we are complex continuums of intersecting lines of becoming- animal, human, technological, oneiric, material- forever shifting and aggregating and coming apart in an extended quantum field. This is the body without organs, in essence: viewing the self as a continuous series of shifting assemblages of intersecting transverse lines that create temporary congruences and resonances that then generate more connections and differences and multiplicities. For Deleuze, the universe is an extremely busy 'machine' which continuously produces an abundance of different connections.
Deleuze explains this connectivity through his reading of the Nietzschean 'eternal return'. Nietzsche's eternal return has been seen as some as the ultimate test of 'amor fati'. Would you gladly relive your life if you had to do it all over again in exactly the same way, reliving every detail? Deleuze however, reads it slightly differently. Deleuze uses Nietszche’s concept of the eternal return, but only to show that what returns it not the same, but 'difference in itself'. What recurs for us, over and over again, is more difference, more multiplicity. We appear to be solid and consistent, but we are not. Rather we 'flicker' into being like a zootrope, a seeming solidity that is actually infinitessimal moments of return. We return, but with a difference. You can either be active and affirmative of this return, embracing its uncertainty by rolling the dice over and over again knowing for sure that difference is the only thing that is guaranteed. Or you can become reactive and negative, losing yourself in ressentiment, reading the return of difference as the cold uncertainty and chaos of meaningless existence. Both are ethical choices.
This is why Deleuze placed such a huge emphasis on art and thought. He saw them as the only activities in which the full and positive play of difference-in-itself could be explored. Only the artist gets to fully play the paradoxical game of uncertainty, of difference-in-itself and multiplicity as games of abundance and overflow. Time cannot be reversed and experience can not be grasped directly, but one can, through the magic of cinema and literature, create models of experience that are somehow more than the original experience. This explains his fascination with both cinema and Proust.
So what are Deleuzian ethics? Well, it requires a complete rethinking of subjectivity. You can't think of yourself as one thing, or as the emanation of a fixed essence. Nor can you really think of yourself as beholden to a transcendent power that somehow holds sway over your actions. You have to start thinking of yourself as an assemblage, a convergence of the infinite lines that result in you as you are at this moment reading this silly answer. Then you have to let go of it and do it all over again, moment after moment after moment. Continuous arising from a vast field of which you form a part but which also extends far beyond your understanding. To my mind it is a very contemporary rendering of early Mahayana buddhist models of interdependence and codependent arising of the self from 'emptiness'.
One of the consequences of viewing the world in this way, I've found, is that you tend to become radically individualistic. Experimentation and freedom become paramount. You need lots of freedom in order to construct your particular body without organs- your extended continuum of thought-action-doing-becoming - without being weighed down with dogma. You are not separate from anyone, but your position is always, by definition, unique and continuously evolving. You become less interested in beating other people over the head with your particular idealisms. You start to understand that the universe simply doesn’t work that way.