I was in the recent Guild Wars 2 Beta weekend, which gave me some more insight into the game, and also revealed some things I wasn't entirely aware of. Some was very easy for me to grasp because of my time in the original Guild Wars, others less so. I'm going to briefly talk about some of those today.
For the most part, the game functions in a relatively intuitive manner. Certainly you won't squeeze every ounce of enjoyment and understanding out of it without some time spent on it, but you can easily understand the basics of using skills, moving, quests, leveling, bags, vendors, and gear. With the exception of questing, nothing really strange has been done with these things to make them alien to the experienced MMO gamer. And then there are a few things that aren't quite as you'd expect, and it might take some time to figure out. Here's a few I noted.
There are no gathering skills. Everyone can access any resource node and get stuff from it, even if other people have already done so. It's nice of them to completely circumvent the mine stealing option. But when you first run into a resource node in the game and right click on it, it'll tell you that you can't. Sorry, no tools equipped for it.
This is fine. I'm accustomed to needing tools for mining and the like, but finding the tools was an outright pain. Don't bother looking around the crafting trainers, because they don't carry those. You'll buy it from a merchant, but not all merchants are equal, despite all of them being simply labeled "Merchant." I found the merchant who sold these items - one each for gathering ore, wood and plantlife/crops - near where I initially entered the game area after the introductory event. Once you show up, just look at the nearest merchants and they likely will carry them. The bright side is that you have an equip slot for these tools, so they don't take up space in your bags.
What you might not be ready for is the number of uses. With so many of the traditional money sinks missing from this game, they add new ones. In this case, each gathering tool has a number of uses to it, and once it has been used that many times it ceases to exist and you need to buy another one. They have 50 or 100 uses each, so you don't need to have several of one type on you at one time, but you will need to get new ones.
You can obtain crafting materials from nodes and as drops from mobs, but you will also be able to get them by scavenging gear that drops. In order to do so, you need a Scavenging Kit, and, like gathering tools, it has a limited number of uses. This existed in the original Guild Wars, so it will come naturally to those who are accustomed to that game, but it'll be new for most everyone else.
It's fairly simple. You double-click the Scavenging Kit in your bag to activate it, and then click on an item in your bag that you want to scavenge. It will then be broken down into appropriate component parts, usually ore, leather or cloth. But wait, there's more. With more advanced, and thus more expensive, Scavenging Kits, you have a chance of also getting an item from the scavenging that will allow you to apply stat bonuses to other gear. As you gain in levels and cash, you'll be focusing on this as well.
Scavenging kits can be purchased from merchants for cash, and can also be obtained from most Renown merchants for karma.
When you create a character, you can dye their outfit to match your tastes. At any time in the game, you can modify the color scheme from the Hero screen. Just click the eyedrop icon and it'll open up the familiar dye screen. Simple and accessible!
When you first start, though, you have a very limited palette of colors to choose from. You'll want more options eventually, especially since such popular colors as White, Black and Blue are not available at start. There are two ways - that I saw - to get new colors. The easiest and fastest is buy purchasing them from the gem store, which is the cash shop for Guild Wars 2. Pay cash to get gems, or buy gems with gold, then buy dye packs in the shop.
You will also be able to obtain new dye colors just by adventuring. Sometimes a mob will drop something called a Dye Seed. You can then take that seed to a Dye Merchant, which can be found in your home instance. Give him the seed, maybe pay some cash (I don't really remember if I had to pay) and he will begin making a new dye. This takes some time to complete, 24 hours in the beta, and when that time has passed you will receive a random dye color to add to your collection.
Sometimes mobs will drop something called a Mystic Chest. You'll see it and be very excited, as it clearly holds awesome goodies for you. What it does contain is a random item(s) that you might be able to buy in the gem shop. Neat! But then you'll notice it's locked and requires a Mystic Key to open.
This fits vaguely with an old conceit from the original Guild Wars. Each area of the world had lock boxes you would find, and you needed an appropriate key to open it, which you could buy from a local merchant. They really understood their money sinks at ArenaNet. In Guild Wars 2, though, you can't buy Mystic Keys from a merchant at all. You receive a small number by completing some personal story quests, but not nearly as many as you will likely get chests to match. I had 4 Mystic Chests when I got my first (and only) Mystic Key. Your other option is to buy them from the Gem Shop, or to buy an Asuran Butler Golem and have it open the chest for you.
Whatever I Forgot
I'm sure there's a ton of things like this out there, but these are the ones that stood out to me at the moment as things that people might not clearly grasp at game start. I hope this is useful for you!