Just been looking at more pictures (Autosport-Atlas Subscriber)... the little bits of bodywork under the lower suspension arms go into turning vanes.
The nose reminds me of the MP4-19, and last few renaults too..
theres some interesting detailing on the car, noteably around the upper front wishbones (Where they meet the chassis, the mounting appears curved, I guess to aid flow off the front wing), and on the rear impact structure. It looks like it forms into a small fin on the top light (when you see the pics you'll understand
)
One intersting thing to note, is that they haven't gone for a secondary loading point on the rear wing. The new Renault and Ferrari have gone the Toyota (single post) and B.A.R (double post) respectively. Looks Mac are still using the endplates to transfer the load from the upper elements.
Sidepods look more extreme now. Not sure if thats a by-product of having smaller inlets for the V8's though, but they do seem to have an even steeper undercut than the 20.
All in all, a logical looking progression over the 20... so it should be FAST