There are some effects that notoriously work only on rather specific combinations of screens AND cables. Those look horrible on emulators.

Usually it is effects involving transparency, some games for example literally rendered some things only on some frames and not the others, to achieve 50% transparency, others tried alternating scanlines, or the most crazy one: Sonic that made a transparent waterfall by relying on the fact that cables common at that time blurred pixels horizontally, thus it renders one column that is water and one column that is not, and hope they will be blurred into one single column that is 50% transparent water on top of the background.

Screenshot of the waterfall effect: https://i.ytimg.com/vi/1cGAP1i_4xQ/maxresdefault.jpg

Can't be shown with a screenshot: Axelay. I never seen that game running on a real CRT to compare, but on emulators that game look horrible, with distortions and flickering things everywhere, I was told this was not the intention at all, instead they relied heavily on CRT hardware to create pseudo-3D and transparency.