Wow, that rear wing! A lot of development has been going into that. Yet, the actual wing is completely straight, as is Ferrari's. All others have curved wings, so I expect some other iteracies there as well during testing.
Apart from the rear wing, the sidepods and engine cover stand out for me in the sence that the sidepods themselves are very small, but also the whole engine cover is very narrow from sidepod to rear axle. Look at the amount of space here:
I think it might be just as skinny as the Mercedes.
I agree that the front wing is not much more than a widened version of last year's front wing, but the pylons are interesting.
Besides these aspects, all seems very basic. The floor in my apartment has more development gone into it than this one. I also think that this is just a very basic concept of their bargeboards and doubt if we will ever see them test with them, let alone race with them.
All in all, we have seen the basic concept of the new car and it gives hope for the nearby future. I for one am really looking forward to all the aero development we'll see in testing. One thing's for sure: although Ron is gone, some of the secrecy around the McLaren is still there! And I like it!