I like Flash, though I've only used it to do progressive video streaming and a few other minor text spins on a page. I don't like Flash's IDE. Flex's eclipse might be better, but I did one check of it and it didn't offer full intellisense (even though it is advertised as such), so at the time I decided to back burner learning Flex.
Well, I'm glad I did. Flash 10 supports quasi 3D, but it looks like Silverlight will support full 3D. Read towards the end of Scott Guthrie's Blog here-
Very signifigant. I've been looking for the holy grail platform to do browser based game development for a long time. Flash works, but you have to hack at it. And you don't get true 3D. MAYBE, just MAYBE, Silverlight 3 will be the killer web game app, as well as business RIA creator, that I've been waiting for.
After Christmas it is time to start diving in to Silverlight.