In a sentence, punctuated equilibrium vs. steady rate evolution. I haven't read every edition of the Origin of Species, so I'm not sure if Darwin specified PE in his original theory, but it's my understanding that pretty much all current supporters of the theory of evolution (myself included) support the idea that evolution occurs in rapid bursts followed by long periods of stasis. (I have read also that Darwin made the idea of PE pretty clear, but again, I have not read that myself in his writing, and I don't want to cite a second hand source. It's immaterial anyway.)
This model makes sense to me since evolution is driven by changes in environment, which (often) occur rapidly (on the geological timescale). With that model in mind, what would we expect to see in the fossil record? Well, exactly what we do see.