Just a note for a younger generations that Flash (re-branded by Macromedia as Shockwave Flash) and Macromedia Shockwave were actually two different products - Shockwave being a more advanced multimedia platform inspired by Flash, which was primarily the svg animation tool. Still, Flash was a far more popular format and it was what the most of people used everyday as it was available by default as a plugin on every new browser.
And the user experience was incredibly different. For me personally, when I went to a website that used Shockwave I would reach for the back button because it rarely worked on my machine, similar to RealMedia player and Java applets. Regarding Java applets, I was tasked with fixing one Windows machine in a university computer lab that simply would not load a Java applet. All the machines in the lab were cloned from the same image and I was the resident Java expert. For the life of me I could not get that machine to load the Java applet - I spent an entire day on it.
Flash always seemed to work and load fast which likely had some role in it getting mass adoption.
The distinction I remember from the time is that Shockwave player allowed 3D games (a use case that was later also filled by Unity Web Player) while Flash Player was just for 2D stuff. Also, Shockwave and Unity weren't available on Linux, unlike Flash.
