Huge improvement over Mk 1. The fact that Roger is using new test charts makes it impossible to really compare it to other lenses, but, still, it is significantly better than the 100-400 II and 400 DO I.
I would expect that with all Canon's efforts with DO that this will be a belter of a lens - I mean a really sharp relatively lightweight 400.
If this sale good, more DO lens will coming shortly,I hope 70-300 DOII that have similar IQ as 100-400LII
The 400mm range is really crowded in Canon's line.
I think the only way this lens is going to sell really well is if it proves to be essentially a 400mm version of the 300mm 2.8 II; that is, a lens with just legendary sharpness. Otherwise, I don't know how you justify the almost $5000.00 difference between it and the new 100-400. So far, it's looking as though it's more than somewhat better than the 100-400 in the center and phenomenally better at the edges. But until we see some shots from the field, it's hard to say how that translates in actual use.