The fundamental concept of the game is identical to all the PSOs and Phantasy Star Universes past: adventuring in enclosed, semi-random dungeons in a sci-fi setting, as some kind of hunter, mage, or ranger character of your own design, with a variety of weapons like beam swords, rifles, and knives. But Sega has retooled the mechanics in a way that no PSO game has dared to. Where previous games had strict, rhythmic, timed three-hit combos, PSO 2 mixes it up, allowing you to continually use light attacks, and throw in heavy attacks as long as a rapidly-refilling "PP" meter isn't empty. You can even jump now, and employ jumping attacks. You also have a dash move, which further cements the "action game" feel.
The monsters also aren't as stilted as they used to be. Instead of slowly lumbering toward you as most PSO monsters do, even the basic sasquatch-esque enemies run and swarm you, in a manner that justifies your suddenly deft movement and combat abilities.
You'll need those abilities in the new boss sections, which bring 12 people together to face a big monster, in this case one of the series' signature dragons. We all swarmed the beast, swinging our swords at its feet, spiky tail, and head for what must have been about 10 minutes. I frequently had to heal myself (items are mapped to the keyboard, and can also be set to a macro on a gamepad -- the game supports pads and mouse/keyboard controls), but after a lot of damage from tail swings, attacks from underground, and fire breathed on us (which leaves you in a "burned" status that saps your HP for a few minutes), the 12 of us completed the task we had gathered in Sega's booth to achieve. It was like we were the Fellowship of the Ring, except sitting quietly in a convention center in Tokyo instead of trekking to Mordor.