I attend Sakuracon and Kumoricon annually. They're great, but you really have to know how to enjoy them. That is, the kinds of events to look for, the kinds of people to associate with, ext. For instance, any panel with an "18+" tag on it has a 90% chance of being awesome. Especially if it takes place late at night and there's nothing scheduled after it, so that there's the potential of it running longer and turning into something godly.