I do not use notion so i cannot comment on cool stuff in notion.
The Obsidian plugin I use most by far is the excalidraw plugin.
It allows for you to embed drawings made in excalidraw.com in your obsidian vault. this is how i do notes like this for chemistry:
Excalidraw allows for you to get back a lot of the freedom that is lost when switching from paper to an electronic medium. Using excalidraw means i do not have to set macros for all the various unicode characters i might need to type, as I can just draw them.
The only disadvantage to this is that the contents of the image backgrounds arent searchable. My annotations upon the images are searchable, so if i wanted to search for “calorimeter” that drawing would pop up, but it does not run OCR on the images to do embeddings for search.
The Excalidraw also allows you to insert any file from your vault into the excalidraw drawing, so I import a pdf into them for chemistry, but you really could do just about anything.
Another nice obsidian feature is their vim mode, along with vimrc support through a community plugin. I love modal text editing and if it did not have vim support I simply would not be using obsidian.
I also like the Custom File Explorer Sorting plugin, for when I want to make a folder not be sorted as the top item in a directory, though this will not apply to my quartz instance, as it does not have this plugin when it generates the html files.
I also like the omnisearch plugin. I believe it does a much better job than obsidian’s native search at searching your notes effectively. It is also faster in my experience.
The Pandoc plugin is nice for converting my notes to different mediums to send to people. ( pdf, html, ePub, etc )
The various sharing plugins are nice for giving a person access to just one note without giving them access to all the notes. I have yet to see any of them support images though which sucks.
HTML Reader is nice as I can just throw full html files into my obsidian vault and read them later or embed them into excalidraw documents.