Gemini is a protocol for distributing a type of markup called gemtext which is based on markdown. The basic idea is that it is an alternative to the world wide web that is entirely composed of simple text pages. CSS is not a thing in Gemini - all pages look the same.
It is really cool. The pages are really small (data wise) and the consistent, customisable look is really nice.
That said, I have problems with it.
Firstly, and most obviously, Gemini does not support inline links. This is a bit of a problem for me because I am quite fond of them but I could adapt and I think that there is a valid argument for having links on their own line.
More of a problem for me is the lack of emphasised text because gemtext has no inline elements. This decreases the semantic meaning that can be conveyed compared to markdown or HTML which seem to me like a unnecessary sacrifice on the altar of minimalism. There are also only 2 levels of headings.
This dedication to minimalism seems to not really to be shared by the users who use various annoying hacks to approximate the abilities of the web. Writers deprived of header images adorn their pages with a surprising amount of ASCII art. Now I’m not saying that there is anything wrong with text-based art however it is terrible for accessibility and usability for readers in almost every way when it is just shoved at the top of a document with no way to separate it from the rest of the page.
I’ve even seen a elaborate replacements for horizontal rules (which are not in gemtext) made with letters arranged in a squiggle shape.
I think that Gemini could have been really good but it was let down by its focus on minimalism at expense of its promise of usability.