Video playing has decent coverage, but Flash games and apps aren't going to work. Once in a while I get an interactive diagram I'd like to use, like the midterm elections app in the NYT, so I had to wait till I was using a notebook to use it.
I was surprised at the number of sites I could play video in a browser.
See here for a list of sites that use html5 with the iPad in mind:
http://www.apple.com/ipad/ready-for-ipad/
I miss having Flash, but not that often.