I wasn't in this playtest as I actually bought mine outright, but I have this to say. Adidas struggled constantly to match the excellence of the Barricade II and III and still to this day hasn't gotten it. Babolat, however, had their great shoe moment with the Propulse 2. They made a softer and yet quicker version with the Propulse 3. The Propulse 4 feels like an exercise in engineering. Instead of with the 3s where the weight feels as though it's in the sole, the extra rigidity of the shoe makes it feel as though it's perfectly balanced.
So, in other words, it combines all of the great features of their prior shoes, and leaves nothing out. As someone who has owned 5 pairs of Propulse 2s and 6 pairs of Propulse 3s, my first pair of P4s is simply a different league of shoe.