It's not pixel-art. All their "entities" are actually 3d models that are rendered into isometric images. And they've also slowly been regenerating all their images with high-resolution models + renders.
Which makes it better than the 3D you yearn for. You can't do as high-quality and as stylistically consistent graphics with real-time 3D rendering; the computing power simply isn't there.
Pixel art means making a picture while zoomed in to see individual pixels, placing them manually nearly pixel by pixel (only the most basic shape tools are used, and no anti aliasing).
