The world of Tyria
Graphically the game looks brilliant, the effects when you cast spells, how the people look in the game the detail in the armour and weapons and the water and its reflections look ace.
The sound in the game is pretty good, it offers nice background music that doesnt get to the stage where youd wrather tear your ears off your head than listen to it again, which is always a good thing but it wold have been nice if it varied for when you got into a fight.
The system Arenanet came up with, where instead of having to shut everything down for a day to patch things like WoW the updates are constantly streamed to you as you play and if a certain area has been updated when you go to enter it will load those updates in on a load screen.
I have never really had any real problem with lag on Guild Wars and the game is extremely stable, only once since the game has been released has it crashed and the problem was fixed in around an hour, if you ask me thats pretty impressive for such a large game, holding so many people.
The team system has been improved as the last update and now finding a party is easier, before you had to stand in an outpost and put the whole "LFG for blah" now a system has been introduced where you can state your class what you are looking to do in the area you are in and if someone else is looking to do that you can invite them or ask them to invite you.
Also another system that has been brought in is if you get an error or you crash, loose your internet connection whatever, if you log back in within ten minutes of this happening you will appear back where you were.
Guild Wars was the first MMORPG i ever played and i played since release date and im still playing now two updates later and all and it still offers the same good quaility of gaming.