It has become the norm that teams reveal their cars with pictures and clips of renderings, rather than unveiling the actual cars, in order to reveal even less technical details than what would be visible on a real car.
Nevertheless, brightening up the released image does reveal that Williams' new car features some interesting changes compared to the team's car from the last few years. While ignoring front and rear wings, mainly because they will change anyway in the upcoming tests, the most obvious change as the front is the neatly integrated S-Duct along with a sharp kink where the nose cone and the top of the chassis meet. This is much like what could be seen on the McLaren MCL22. The result of this is that the front bulkhead is now marginally higher up, clearing some space underneath the chassis for better airflow. To further enhance this, Paddy Low has likely been an influence to introduce a Mercedes-style "cape" underneath the nose cone.
Further back, the barge board and sidepod entry area seem to be a lot like what Ferrari had on their 2017 car. The inlets are wide almost as high above the ground as possible, feeding all airflow that was worked upon by the barge boards towards the rear of the car, and help the diffuser to do its work. The barge boards themselves also see a new large panel, also similar to Ferrari's 2017 design, but attached to the car by an aerodynamic wing that helps condition the airflow that will eventually end up flowing into the sidepod inlets.
Other obvious changes is the new airbox design, with an oval entry and a large undercut. Here, Williams appears to have taken some inspiration from Mercedes, which is hardly a surprise given they're using the same engines, and hence, the same air intake requirements. There should be no doubt that the changes are also fuelled by he introduction of the Halo as that is disturbing airflow in their area as well.
Also highlighted in the image are the double rear wing support with a swan neck to improve aerodynamic efficiency of the rear wing, while a rear suspension redesign has led to a very long pull rod at the rear, very similar to what Red Bull Racing have been doing for a while.
While much more technical analysis will likely be rendered pointless in the upcoming tests, Mark Priestley has some further insights as well: