On Buddhism I find the idea of rebirth utterly irrelevant, unless you were to place your faith in an Atman which persists and aspires to become one with Brahmin (from which it was never separate in the first place). In that sense I think the Vedanta is actually more coherent philosophically than Buddhism. — Janus
From what I understand, Buddhism claims that all is empty and all sentient beings are Buddhas (enlightened), and it is only our ignorance (of our true empty nature) that prevents us from realizing this. There seems to be two ways to know emptiness: intellectually and experientially. Personally, I think impermanence is the key to understanding it intellectually. If everything is in a constant state of change then there cannot be static or independent things. If something was completely fixed and independent, well, it certainly wouldn't be alive.
As for knowing emptiness experientially, that can happen deliberately as with some form of contemplative practice, or it can be experienced unintentionally by something (such a stroke, see Jill Bolte Taylor) causing a particular brain state, or perhaps with the use of psychedelics. In any case, it is still just a transient experience. It may have benefits, such as relieving existential anxiety and whatever else, but these benefits may need to be maintained by regular practice.
From this perspective "enlightenment" doesn't live up to the hype, but it does explain why we don't see any enlightened people walking around, being all all-knowing, all-loving, all-compassionate, all-unsuffering, and all-whatever-the-hell-else-some-priest-can-dream-up.