With the changes to Java over the last couple of years, I would say it offers much more than Flash does. However, the biggest drawback to Java is the size of the client you need to download.

Personally, I think many users (especially dial up users) would just move on rather than download a 10MB client to play your games. If you want some feedback on what Java can do, check out javagaming.org

However, my personal opinion is that Flash still controls the online game market simply because of it's small client.

borngamer