Now that we talked about vi we can talk about vim and nvim. I am going to group nvim and vim together because most of the fundementals dont change and the parts that do change can be explained pretty easily. Note all things in vi apply to vim/nvim.
Text objects
This is one of the most interesting points of vim which is rarely in other text editors for whatever reason. Text objects are well text areas based on what keybind associated with it. So you can do diw to delete the inner part of a word text object. People using vim tend to not realize that the i changes the next character (w in this case) to do something completely different but the same based on pnumonics. I didn’t even notice that this was different because dw should actually go to the beginning of the next word but it doesn’t and does what de is supposed to do.
The amount of text objects have is actually nuts and not even vim does a good job with them. Text objects not only could effect simple things like words and stuff inside parensthesis but actual structures inside code. Vim lacks the support to do this without plugins and it would depend on the language so they don’t do anything like this. Vscode and other editors aren’t modal so it becomes much harder to add text objects as they require people to memorize multiple keybinds and its harder to get someone to press a modifier keybind twice (just as bad to do 1 modifier keybind and one not).
Scripting language
This is one of the parts where vim and nvim differ. Vim introduced vimscript as a custom language which could extend the vim text editor. While vim is great for setting up your configuration and vim-like stuff, it becomes much harder to use for complex tasks and tends to be pretty slow. After the main dev of vim refused to add certain features and address certain things nvim was created. When nvim was created they decided to rewrite vim (still supporting vimscript) but some things including better defaults and 1st party support for lua instead of trying to fix up vimscript. Note they still will support vimscipt just they will try to phase it out. Addressing the issue of vimscript being slow the creator of vim began creating vim9scipt which is not backwards compatible but significantly faster then vimscript. This is where we are in the current moment of time.
Now that we got that out of the way vim is mostly written in c but has a significant amount of vimscript so you can configure it and extend it. Vimscript makes it easy to run commands when certain files are opened, set keybindings, set settings and much more. Having nvim support both lua and vimscript allows for complex plugins to be made in lua. I believe there are multiple plugins that use this lua and could not be created without the lua support.
Lastly the scripting language makes it easy to add plugins and because vimscipt/lua is so good, there are many different plugins that do interesting and useful things. From everything to build systems to lsp to adding new text objects there is a plugin for almost anything.
Macros
Macros in vim is again amplified by modal keybinds and the workflow of vi. Because everything you do in vim tends to be percise, you can setup macros which move arount the structure of what you are editing easily. I do not do them because it is very complex but you can also do recursive macros and because macros are just plain text stored in vim registers, you can just make one then paste it in your config for later.
Misc nonvi features
vi is very basic so vim has much more modern things such as multi level undo, syntax highlighting, visual mode, more cross platform and more. The multilevel undo is pretty good because of the sheer amount of things you can do with it. Also basic support for programming with ctags.