They've tried to keep the quality of the game up and it shows, as the number of zombies is doooooown. So you can argue until the cows come home that graphics do not matter, but in this case they've sacrificed zombie count (as far as you can tell from the screens) for visual quality, thus ruining gameplay in favour of graphics.
Of course this is all based on a handful of screenshots. I reserve final judgement until any screens of the car park are released- that will show us if they can pull off hundreds of zombies at once.