Andrewsarchus and Uintatherium, to name but two, are closer to the flippin' dinosaurs than they are to the Pleistocene. I love the beasts of the ancient Cenozoic, but I like some realism in the style (a dire wolf that looks like a genuine dire wolf would be nice, for example; it's only the best-preserved of all prehistoric animals, after all). These are just too Scooby-Doo for me.
A lovely idea I would've loved to back, but I'm not a fan of this kind of execution.