I think to clear things up just a tad..
Almost all of the interaction with other people in Guild Wars is done in the various outposts,towns, mission sites, or your very own Guild Hall. You can easily see hundreds of people in towns. Since the game is played on one server that is shared by everyone, ArenaNet introduces districts for towns, outposts, and missions. It helps cut down on the bandwidth. People are always moving between districts (its the same town, same looks, just a different set of people) so if you have a friends in Lions Arch District 1 and you are in Lions Arch District 2, you can meet up with him by switching to his district.
As soon as you leave a town and enter an explorable area or into a mission, the only ones in that zone is YOU, whatever party you have brought to fight along side of you, and the foes. This makes the game more personally enjoyable.
As far as the whole Faction thing goes. There are two types of Faction. There are Balthazar Faction and there are Luxon/Kurzick Faction. Balthazar Faction are essentially "points" you earn alongside experience for doing PvP type of gameplay. When you earn enough of these "points" (which are earned a various number of ways), you are able to unlock more skills/inscriptions/heroes to use in PvP play. The more skills and things you have unlocked, the more options you have. Kurzick/Luxon Faction on the other hand are a little different. To gain these "points", requires you to have Guild Wars: Factions. Not to give anything away, but the one of the main features in Factions is the struggle between two huge alliances: The Kurzicks and The Luxons. The guild you are in is usually sided with one of the two and there is an "every-going" struggle for Canthan territory. Alliance Battles, which is a toned down "PvP" type of gameplay, pits 12 people from each alliance into battle. Ownership of territories and towns in the game are shifted depending on which side has the majority of the wins when the game checks the records.
As far the classes, there are 6 core classes (Warrior, Elementalist, Monk, Ranger, Mesmer, and Necromancer). If you get factions, you can add the Assassin and the Ritualist to that group or in Nightfall you have the Dervish and Paragon. Each class offers unique skills and requires a different type of gameplay. Some things you may find similar to other games, while a lot is different. When you start the game, you are given 4 character slots to start off with, so you can choose a couple and see how they are. Trust me..........what you read on any forums, manual, or any review, each class is a lot of fun to play. A lot of times you have to think. This goes for both PvE and PvP. A lot of failure and success is based on people's judgment (or lack of).
If you'd really like to get an idea on what guild wars is really like, definitely get a Buddy Key. Its basically a Free Trial which allows you to play for 14 days or 10 hours (whichever comes first)....and trust me...the 10 hours always comes first. There are plenty of sites and Forum topics that OP have listed that are helpeful on answering a lot of newer people questions or to find out what the game is all about. You should definitely take a few minutes and check them out and see if Guild Wars is definitely the game for you. If you have any other questions, feel free to ask.
- Aldoros of Faydark
(whew.....my novel is complete)