One of the key elements of GW2 that helps to make it differ from other MMOs is that weapons have the skill sets, not the person to a degree.
What do I mean by this statement?
1) If you are a warrior with a sword in the main hand it will have a different group of abilities to use then say having a mace in the main hand.
In traditional MMOs no matter the weapon you get the typical #1 attack, then the #2 special attack with a #3 super special attack. With #3 taking much longer then the previous two to cool down. The a fore mentioned attacks are exactly the same using a sword or a mace, or any other weapon. Just different animations to a degree. That is not how it works in GW2.
In GW2 with a warrior using the sword in the main hand you will have up to 4 attacks. a) flurry; b) sever artery (first step in a chain attack); c) savage leap (closes the distant to your target [range attack]); d) hamstring (cripple attack). Most of these attacks cause a target to bleed.
Now said warrior uses the mace in the main hand. Again up to 4 attacks. a) skull crack; b) mace smash (first step in a chain attack); c) counter blow; d) pommel bash. A couple of these attacks cause a stun.
2) Now lets compare a warrior to a guardian. The first major difference. The guardian only get three attacks compare to the warrior's four.
Now look at the warrior with the sword in the main hand above and compare to the guardian with a sword in the main hand. a) sword of wrath; b) flashing blade [range attack]; c) zealot's defense [range attack].
Now the guardian with a mace in the main hand. Again compare to the warrior with mace above. a) true strike (first step in a chain attack); b) symbol of faith [AoE affect + to allies - to foes] ; c) protector's strike [AoE shield].
Each weapon as you can see has it's own attack group and varies between the professions (classes) as well. There are a total of nineteen weapons in the game including a shield, warhorn and a torch.
Yes I said a torch. It is an off-hand only weapon and is used as one by the guardian, ranger and mesmer.
Three of the nineteen weapons are for underwater combat as well. Don't worry about learning a breathing spell or carrying a ton of potions that allow you to breath underway either. You start out with a breathing mask which equips automatically when you go underway. But I digress, the weapons are the harpoon gun [range attack]; the spear and the trident. Again each with their own type of attacks that vary per profession and weapon.
When you also add the fact that you can swap weapons while in combat (see my earlier article "Guild Wars 2 weapons swapping on the fly (sorta) for the uninformed"). It makes this a game where you are going to have to think out your attacks as well as pick weapons that suit your personal playing styles.