Flash has a bad rep in the tech press. It resurfaces whenever Adobe updates the player plugin, which is the only part they actually control anymore, or when the discussion turns to Flash content on mobile platforms. And it's not wholly inaccurate, but it's way out of proportion to what Flash deserves, and what it achieved.
Even so: let's pretend that YouTube, decent APIs, and speed aren't important to us. What's Flash got going for it? As XKCD pointed out, it spawned a tiny renaissance in simple, fun, 2D gaming. As a tool for making everything from the sadly-departed Scrabulous to Alien Hominid, Flash provided a slick platform allowing artists and novice designers to experiment and get exposure. It's done for 2D what Duke3D and Doom did for the mod scene. Say what you like about it, if you love retrogaming, Flash deserves some credit for its recent success.