Nearly all gray, with flat black, no gradients to smooth anything. Gives the impression of harsh lighting.

Very sharp-edged 3D boxy window design creates heavy cumbersome feel.

Inconsistent pixelly fonts.

Oddly aligned text in button.

Diamonds happen to be a shape that maximizes pixelation.

Indent in vs. out is cognitive heavy to process, relative to something less pure-dual.

Black selection border doesn't have consistent widths.

Separation line between big button and little buttons, despite obvious size and shape differences that already make that distinction.

Extra little borders defining window box corners from horizontal and vertical borders - a distinction that surely didn't need highlighting.

No rounding. (Granted, rounding would look pixelated.)

TLDR; It looks like an industrial lead brick you really don't want to drop onto your foot.