Like web browser and the OS itself, it comes under attack occasionally. You’ll hit pages you want to go to that won’t work without it. It is hard to use an enjoy the web today without having the Flash plug-in installed. But how is that “intrusive?” If you go to a web page that has a game, or a graphing app, or a video player, how is that intrusive - presumably you went to that page to use that app.
Flash can be used to create some great interactivity on web sites. I’m not sure what you mean by “intrusive” in your question. I’ve written books about Flash game development. I spend most of my day programming in Flash. I have many Flash game sites that I have built myself. But that is true of web pages in general, not just Flash. There are also those who seek to use its power to do harm. Being an environment where developers can create apps, there are developers who can create very useful or entertaining things with Flash. Nothing is completely safe - using your browser, surfing the web, using your computer at all. The question of “is it safe” is not a straight-forward one. A Flash app in a web page can be as simple as an animation or audio player, or as complex as an office suite of tools. It is used to build interactive applications into web pages, such as games, video players, presentations, work apps, just about anything. Adobe’s Flash web browser plug-in has been around for a long time.