I think Flash was fun to develop in. It was easy and fun to write a game in it and it was something a lot more approachable and easier to distribute than trying to cobble together something with OpenGL or DirectX.

Also, I think a lot of the games on Flash actually are fun. I played through Mystery of Time and Space a few months ago and it still holds up. The puzzles are clever, the jokes are funny, the art is likeable, it's a good game.

But what I liked about Flash was that, because it was so approachable, there was a lot of creativity to stuff. A lot of the games weren't good in any kind of "objective" sense, but there was at least a distinct lack of cynicism with a lot of them. The people who made the games weren't doing it for money, they were doing it because they thought it would be cool to make a game. Some games, like Pico's School for example, were unlike basically anything that had come before it. Is Pico's School a masterpiece of game design? Nah, but it's certainly unique, and it was something that could be played on pretty much anyone's computer.