There's definitely a criminal lack of content. You finish the Main story, theres I think 9? Shrines and 3 towers, all relatively short as well with varying degrees of difficulty. PSE bursts seem to be the only current 'endgame' if you can call it that, aside from the standard Alerts like they had in the original PSO.
Its a shame too, cause the game and combat is really fun if you're not lagging, but once you beat the very short main story its just... yah, theres nothing to do except maybe farm 4* Weapons in PSE zones.