With this post I want to briefly detail PvP (Player vs. Player) in Aion. Aion is primarily a PvP-centric MMORPG. That is not to say that the end game only consists of PvP, but that the game was built and marketed as PvPvE. This means that while the game does have a PvE (Player vs. Environment) aspect, it is heavily intertwined with PvP.
The first and main example of this is The Abyss. The Abyss is a huge area that goes from the mid-20s until max level. It is an open Faction PvP zone, meaning that the two factions of the game (Elyos and Asmodians) have free reign to attack one another. NPCs here grant more experience than elsewhere in the game because of the added risk of PvP.
The Abyss contains a number of castles which can be held by guilds, called Legions in Aion. Players battle both NPCs (guards) and enemies of the opposite faction assuming they are there to defend their castle. Control of a castle gives players of the same faction access to special goods, as well as bonuses for the Legion who controls it. There are also end-game dungeons within the Abyss, both instanced and open (meaning players from both factions can be inside the dungeon at the same time). This means that players going into open dungeons not only have to worry about the PvE aspect, but that they may be flanked by the opposing faction at any time.
Another example of PvPvE in the game are Rifts. Rifts are portals which open randomly (in 20+ zones) that give access to the opposing factions areas. Players are free to enter the rift and attack anyone on the other side. Rifts have a few limits. First there is a time limit. If you are caught on the other side when the rift closes, the only way back is to die, use your Return spell to get back to whatever zone you are bound to, or via a portal summoned by a Sorcerer. There are also level and number limits. This means that you cannot have 200 people pour through a rift at the same time. This was presumably done to keep the odds from being too overwhelming. At the same time, the level limit means that a level 50 player cannot jump into a level 20 rift and go around griefing lower level players.
The third part with my brief impressions of the game so far up to level 15 will go up soon.