Yes, it can do particles, but you have to code your particle systems from scratch.
Basically you can program whatever you want in Flash, but that doesn't necessarily mean it's going to run well. The more complex your game visuals, the slower it will run. And it doesn't take much complexity to start bogging down.
Frankly, I'm surprised that Flash has become the standard that it is, and I wouldn't mind seeing it go away forever. I mean, who the hell thought it was a good idea to do vector graphics in a browser? Fundamentally it just doesn't make much sense to me.