I'd say Newgrounds is the modern day Newgrounds. I don't have Flash installed, I went to Newgrounds, and the first couple of games I clicked on worked without Flash while others still required it. If there's new or old content that still requires Flash, then it can be emulated. Here's an example of a large collection of games playable in an HTML5-based emulator: https://archive.org/details/softwarelibrary_msdos_games

As for other HTML5\WebGL focused sites, here's an example of a site making HTML5 games: https://ga.me/

And here are a couple of sites indexing WebGL games:

http://www.webglgames.com/

http://www.webgl.nu/

So don't worry. There's lots of HTML5 game development going on.