So: GW is a game which is kinda different from every other MMORPG. You can really play it in 2 ways: casual player, more oriented towards PvE and basic PvP. You can easily obtain the best armor and items stats-wise in a week more or less. Level cap is 20 so you can reach it in a few days. And stats make a huge difference between starter gear and end-game gear. Good thing is you don't have to sweat much to get them. There are collectors who give you perfect-stats items for really cheap, and some monsters drop 'green' items quite frequently which have perfect stats as well.
Pet classes: basically 2. Ranger: you have an animal with you (pet) which helps dealing damage. Necro: you can raise an army of minions. They're both useful in PvE and PvP, but in the latter one only for specific builds and they're not played by top rank guilds, that's why you might not have seen them. They're generally always good in PvE.
Some quests are repeatable, especially the ones where you get the best loot (Sorrow Furnace, Underworld, Fissure) but generally you can play every map all the times you want and face the monster bosses that drop the 'green' perfect items. You just farm without needing a quest.
No auction system ingame. That's why there's a huge (and the best thanks to the wonderful mods
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) section on Guru about trading. If you wanna trade ingame you just stay in one of the biggest cities and advertise your items in the local chat (there's a specific channel for trading). Also, for materials, runes, dyes etc. there are NPCs traders which buy/sell stuff at market price. Of course there's a consistent gap in the offer/demand so if you wanna make those extra golds then you better sell to a player.
PvP: there are different kind of pvp, ranging from random arenas where basically you train yourself with random teams. Then when you're ready to step up you can just join organized teams. Of course if you wanna get the best from this part you should join a decent guild. The game is really well balanced, as you can easily have the best equipment, so it's really a matter of skill only. You can also just create a pvp toon already at lev 20 and create him with the best gear. Of course he will restrained to pvp side only, so you won't be able to sell its perfect equipment to other players.
GW is really an awesome game, ranging from casual player to pro-player. You can play whatever suits you better, but after a while of PvE you will wanna face the true challenge of some serious pvp.
There's so much to discover about it that a post is not nearly enough; just buy and get addicted
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And yes, Guru is the best fansite. Period.