Skill collection factored heavily into the original Guild Wars experience. Gear had statistical bonuses, but wasn't as essential as armor in, say, World of Warcraft, where the proper gear is required for success. Leveling was deemphasized, and even though the level cap in Guild Wars 2 is 80, leveling isn't meant to be the main focus. It's more a gauge of progress, like watching an odometer tick up on a road trip. Instead, the prime motivation for playing was to collect skills. ArenaNet likes to compare their way of doing things to be more like Magic: The Gathering than Dungeons & Dragons. Your skill set is your deck. Even after collecting what's best, you still need to learn how to use it all properly.
Guild Wars 2 Video Preview
The key to the skill system in the original was that every skill couldn't be active at once. You had to pick which worked best together. Guild Wars 2 builds on this concept. Predefined skill sets are tied to weapons. If an Engineer equips a two-handed rifle, then the same skills will always be active across one half of the skill bar. Assuming the skills are unlocked, you'll get an overcharge shot to knock back enemies, a net shot and a jump shot every time. Drop the rifle for a one-handed pistol and shield and a new skill set opens up. The locked skill set associated with each weapon functions as an equalizer. If you see a player using a particular weapon type, you know they have these base skills. For customization, there's the other half of the skill bar to play with.
For the Engineer, this means swapping out kits. There's a mine kit, a flamethrower kit, a grenade kit and more. When activated, the kits replace the five weapon skills with a unique set. So if you activate the grenade kit, you can toss out poison grenades, freezing grenades and fragmentation grenades for as long as it makes sense. When you're done, you can then quickly drop the kit skills and return to your basic pistol or rifle set. The same goes for the flamethrower, letting you blast out fiery jets to singe multiple targets or set up a firewall along the ground to do damage over time to any immobile opponents.
These kits eat up one slot each, and can be swapped in and out at will until a fight begins, at which point you're locked into your choices. Kits aren't the only way to customize the Engineer's combat experience, though. Gun and thumper turrets are there too, which can be set down in a fight to automatically damage foes and also draw their attention. Since each profession isn't meant to be locked into specific roles, Engineers get heals as well. Some I saw included a basic self-heal as well as a healing turret, and ArenaNet there'll be plenty more to unlock throughout your journey.
If you duck underwater to fight fish and other aquatic beasts, there's yet another skill bar. Engineers can lob mines into the water that detonate after a set period of time, or fling out fishing nets to trap advancing targets, then follow up with a few torpedo shots. ArenaNet doesn't want the underwater combat to be a copy and paste of the land combat, only slower and more awkward. You won't use the same weapons as on land, there's no breath meter; instead you're armed with a spear gun and use skills that take advantage of the extra movement axis.
Lion's Arch Trailer
From what I played, (an early dungeon in story mode), the encounters seem well designed, requiring frequent shifting of skill sets. My group consisted almost entirely of Engineers and we were still able to plough through after a few embarrassing wipes. Enemies would sometimes trigger area of effect attacks and we'd have to roll out of the way. We had to get used to the idea of setting up a mixture of healing and offensive turrets. We had to revive each other in the field, simply by holding a key down near a corpse. Even though there wasn't a true tank, we gradually sank into specific roles: the flamethrower Engineer, the rifle Engineer, the Engineer that drops health packs, the one that goes crazy with mines. Then if bosses did something like spawn hordes of trash mobs to distract us, we could all flip over to flamethrowers to burn them into oblivion before switching back to preferred weapons or kit skill sets.
Outside of the dungeons, questing is meant to be bring people together instead of force you to treat everyone else as a competitor. Inflict a basic threshold of damage upon an enemy and you'll get credit for the kill and share in the loot. Wander into a public questing area and you'll get wrapped up in the task with others, be it destroying a flailing ice worm or destroying a mining tower while enemies scamper from a nearby cave to shoot at you and try to repair it. The cleanly presented map tracks your movement in a zone and makes it easy to identify places of importance. Teleporting between waypoints makes getting around the zone quick and easy. It should be simple enough for any MMO player to pick up, but there's clearly a lot of depth to the customization, especially when you start to consider the tweaks that can be made through the game's trait system, which can further modify nearly everything about your profession.
Based on what I played, taking into considering the combat, customization options and visuals, I have little doubt that Guild Wars 2 is one of the most promising MMOs in development. Someday ArenaNet might announce a specific release date, but for now the studio maintains it'll be done when it's done.