After many years programming graphics in C++ I ended up having to code a big web project during a whole year, it was for the Barcelona World Race online game. Because the project requested lots of graphics and interaction I decided to do it in Flash, by that time I only had made some silly tests in Actionscript so I had to learn fast and not only the basics.
Barcelona World Race
The project ended up being a success with more than 50.000 registered users (surprising for a game so niche as the sailing games).
After that project I felt that Flash was a great platform, performance is good, the API is complete, the official IDE has all I could expect, and the projects can be deployed to web or desktop without any problem.