Mostly that even for something three decades newer, it does nothing with the newness except bad things: it doesn't allow for more than one (1) link per paragraph, if at all. Doesn't have a concept of text alignment, text weight, spacing, italics, underline or any of the other stuff CSS 0.1 inherited from the historical printing press. To my recollection, doesn't even allow you to use any alphabet set that is not English's one (so stuff like math equations are out of the question), and you can't post a link that has international characters (like the wikipedia page for "Ñandú") without hideously percent-escaping them. In 2024.

In exchange, Gemini seems to require SSL and a certificate of all things, which means it's a lot costlier to implement on low-end hardware and it's noticeably vulnerable to tactics like domain seizure because you need a valid cert which means you need an external "naming authority".

Looking at it from a distance, it feels like someone looked a Gopher and went "I wonder how would this feel in the format of a brutalist buttplug".

On the plus side tho, thanks to the lack of anything even resembling formatting, Gemini does realize one thing that I don't recall Gopher realizing in full: rendering of the document is under control of the viewer, not of the author. For good or bad.