1. Antialiasing of fonts, how crisp and clear does it look on my screen? Windows has struggled with this especially after ClearType.
2. Alignment of elements in various applications. The traffic light window controls look way too far into the app's header. Find a happy medium, copy macOS's spacing.
3. Is the contrast in colors strong enough to tell me this was designed by someone who has some design (hopefully color theory background) or was it just an attempt to use many colors?