It has a good PvE storyline to follow or you can jump straight into PvP if you like with a level 20 character.
A lot of people like to do PvE first to unlock many special runes and weapon upgrades that are hard to get in PvP.
Example. In PvE i can find a suit of armour and salvage a rune from it.
In PvP I have to fight and win a certian number of battles to get faction. You can then use faction to buy these rune/weapon upgrades.
A PvE character can do both PvE and PvP. A straight PvP character can not do the PvE storyline missions.
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