Adobe's Flash is used by a continuously decreasing number of game developers. That's a fact. Some would go as far as saying it is already defunct, its place being taken by other environments, such as HTML5 and Unity. Flash has served its purpose - it was the go-to solution for web game developers at all levels. For a long time, it was the only thing used for building browser games. No matter if they were built for Kongregate, http://casinogamescity.com/ or any other gaming portal, Flash was the preferred tool. But not any more.
The first major blow Flash suffered over the last few years was when Apple's Steve Jobs announced the end of support for the technology. In an open letter, Jobs bashed the platform for its waste of hardware resources and its lack of security, among others. To be honest, the number of vulnerabilities discovered in the platform make it a less attractive choice for developers and players alike.
From the developer's point of view, Flash is a failed project, at least when it comes to mobile. First it was Apple that has announced the lack of support for it. Later Adobe itself decided to kill the Flash Player plugin for mobile. Adobe AIR is still available for mobile app creation, but when it comes to mobile browser games, HTML5 reigns supreme. And mobile gaming is expected to overtake desktop and even some console game types soon enough, so it matters quite a lot.
The platform that will most likely take Flash's place in the hearts of developers is Unity. It's similar to Flash in many ways, and it seems to be more in tune with the requirements of today's game developers. Besides, it can be used free of charge for building games and apps (even by companies with a turnover under $100,000 a year) that can be deployed both on desktop and mobile devices - albeit not in mobile browsers at this time.
Unity has an excellent visual editor that can work with most mainstream 3D apps. On desktop computers it can be used via a browser plugin. On mobile it doesn't support browser play, but it is a great tool to create native apps that can be deployed via the platform's own app marketplace. Which is a great thing from a free development tool.