Saying Java sucks or Java is slow is like saying Lord of the Rings is a lousy story because it had lousy bookcover illustration.
From the years of reading Slashdot and more than a decade on the web reading about how people bash Java, it is pretty clear how many people can't tell the difference between a platform and an API. It is worrying how much of these people make up the world's pool of software professionals.
While it is true that Sun dropped the ball on Java marketing and the Swing API, it is also true that Microsoft wielded its evil muscle trying to kill it (how many can claim to have survived such attacks?) in the 90's (anyone remember the 9-year lawsuit that Sun eventually won?) and Java as a platform and ecosystem stalled because of that. As a 20-year software veteran who used to write in C/C++ and assembly, I'm happily making a good living writing real-time graphics apps with Java that runs on Mac, Windows and Linux. Those who bash Java just don't know what they are missing and I'm happy to keep it that way: less competition for me.
Lastly, Adobe Flexbuilder, the IDE that this iReversi game was written in, is based on Eclipse. And Eclipse is written in Java using the SWT API. Eclipse is also one of the world's most complex piece of software that runs on Mac, Windows and Linux. Adobe's marketing should eat its own smelly socks.