How Guild Wars 2 is different than other MMOs

How is Guild Wars 2 different than other MMORPGs?  I think this is an excellent question to answer for two reasons.

1. To inform someone who is considering getting the game how it is different than other games they've played.
2. To inform someone who is just starting what differences to expect as they continue playing.

In no particular order, here is a non-exhaustive list of differences:

• GW2 strongly encourages cooperations between players.  Other games encourage this as well, but GW2 simply does it better.  Two random strangers attacking the same mob get the same loot chance and experience as if they attacked it alone.  For quests, it's extremely rare to find mutually exclusive quest objectives.  For example, if the quest was to gather X widgets, everyone has their own version of the widgets on the ground.  Me picking up a bottle of rum does not prevent you from taking the same rum, for example.  Chests work the same way- everyone can interact with a chest and get their own loot, which is the same amount whether you did it alone or with ten other people.
• Following up on that note, partying is rarely necessary.  You get all the benefits of the above without going through the process of inviting someone and having them accept.  For example, as long as you touch a mob you get credit (xp, loot, quest completion) for the kill.
• You get experience for EVERYTHING in this game.  It's pretty cool, actually.  Reviving people (in your party or not) gives you experience.  Gathering gives you experience.  Crafting gives you experience (it's not uncommon to sit down to a big crafting session and get 1.5 levels of xp).  Exploring gives you experience.  Completing a map gives you experience.  The net result is that you get a game which is very not really "grindy".  There are many different ways to level up, and you could get a whole lot of levels without killing a single mob.
• Following up on that point, the leveling is fairly linear.  It takes about as much time to get from level 10 to 11 as it does from 50 to 51.
• Experience rewards in this game generally scale with your level.  Finding a new point of interest in a low level area might give you 250 experience at level 5 or 800 experience at level 40.  It's still usually a smaller percentage of a total level (at level 5, that vista might be 10% of your level, but at level 40, it could be 5%, even after the scaling) but this is compensated by the fact that higher level characters go through lower level areas faster.
• Areas are "level capped".  For example, if mobs in an area are between level 11 and level 14, and you are level 25, your "effective level" will be 14.  Your damage, health, etc. will be scaled down to be comparable to a level 14 character.  However, you will most likely stll be stronger than a "real" level 14 because you have talents and skills that they wouldn't have access to.  There is no "upscaling" of your level.  If you enter the 11-14 area as a level 8, you would stay 8.
• Exploration is a big part of the game.  Discovering PoIs and vistas, completing skill points and venturing through hidden areas is really enjoyable and often an interesting challenge (not to mention xp).  Additionally, they often lead you to things that more practical-minded people care about: quests, special vendors, hidden dynamic events, and rich gathering nodes.
• Gathering resources in the game is both simpler and somewhat more annoying than in a game like WoW.  Anyone can gather anything, but you need to buy consumable gathering tools of the appropriate tier to do so.
• Crafting is also different than other games.  There are no "gathering" skills.  Everyone can gather anything they like (see above).  You pick two crafting skills (e.g. jeweler and armorsmith) but you can gather resources that you can't use that you can either put up on the Trading Post or keep in the bank for your other characters.
• Leveling your crafting works similar to other games, with a slight twist.  You still gain crafting experience from creating items, and there are still certain points when lower level items no longer give you experience.  However, you gain large chunks of experience for "discovering" new recipes.  Only a small set of all recipes are shown to you- everything else must be discovered.  The discovery system is for the most part very structured, and new recipes are usually quite obvious (it makes more sense when you try it, trust me).  At any rate, discovering and crafting new items gives you much, much, much more experience than repeatedly crafting the same item.
• Threat/aggro in the game is much, much, much more complicated than in WoW, and requires a different set of skills to deal with appropriately.  There is a lot more improvisation and chaos than in WoW, when picking up aggro as anyone other than the tank is considered a failure on your part.
• Dynamic events are spontaneously generated quests that call all players in an area over to complete them.  They vary in difficulty but are almost always meant to be completed in groups.  The hardest ones can require 30+ players to do, while smaller events can be done by a few adventurers (or sometimes even a single one).  The scale of impact can be very different as well, ranging from "escort this pack mule to the next city" to "slay the evil necromancer before he opens a portal to Hell and swallows this world".  Events often change the world in a temporary but meaningful way.  For example, failing to defend a camp from ogres could lead to it being taken over by hostiles, forcing you to fight your way through whenever you pass.  Successful defenses could open vendors that are both convenient for selling but also offer specialized, rare items.
• Skill points in GW2 are a unique gameplay mechanic.  Every class has weapon skills which are not customizable.  However, your healing skill, your three utility skills and your elite skill are all chosen by you out of a set of possibilities.  You earn skill points by either completing in game, one-time events (indicated on your map), or by leveling.  Each one of those activities gives you a skill point to be used to purchase skills.  However, certain items can only be purchased with skill points.  In order to make sure there are always enough skill points available, after you reach the maximum level of 80 you can keep "leveling".  This keeps your level at 80 and gives you no stat improvements, but does provide you another skill point, allowing you to purchase items with skill points indefinitely.