Well, I'm a vet of all things RPG and MMORPG and whatever, blah blah blah. Been there, done that. The semantics arguements here are tedious and serve no purpose except to stroke a few ego's. So, I'll give people here what they really want and stay on topic.
Guildwars is an RPG. While the game design was originally done as a PVP game, the PVE aspect, which makes it roleplaying, was not done as an afterside. Many other RPG games that are online through in PVP as an afterthought, such as EQ, AC, CoH, and many more. As such, the PvP aspect of those games STNK. They are awkward, imbalanced, and if you don't make the "uber" build correctly from scratch you are gimped.
Guildwars designed the character system with PvP in mind. As such, pvp gameplay is VERY balanced. It's PvP that is part strategy on many different levels and twitchines. The strategy is knowing which skills to use and how to build your team with friends. Since there is no 1 on 1 combat, the smallest fights are 4 on 4 with the biggest being 8 teams of 8 players per team royal rumbles.
PvP match types are also random and different depending on which "tier" you play.
Arena style is the small battles. 2 teams of 4 on 4 battles. Nothing is ranked and it is good practice and a place to get your feet wet. Chances are, you will get your butt handed to you many times so don't get discouraged. The key here is practice and learning your playstyle to find the right combonation of class and skills that suit you along with team mates.
The next Tier of PvP is the Hall of Heroes. These are "ranked" matches. While you still practice, doing well counts as your character gains Fame and your Guild gains rank. All of which can be viewed from the official website for all to see. The other side benefit to winning in the Hall of Heroes is gaining favor for your "Country." This game is pitched for America vs Korea vs Europe. Why Europe gets to compete as a whole I have no idea. The point to the favor is that winning in PvP DOES have a small effect on PvE. If your country has is currently the champs in pvp then your country can go into the "specialty" dungeons found currently at the temple of ages for the PVE side of the game. Now, there is no STORY based need to go there. It's like the Cow level in Diablo. It's a fun, difficult, and item rewarding dungeon.
That's it for PvP, now for the PVE or RPG aspects of this game.
Despite this game being built originally from the ground up for PVP, the developers were no slouches in the PVE aspect of the game either. There are cutscences every step of the way. Difficult missions, with a plethora of side missions and bonus quests. They designed the game to work in favor of the casual gamer or the hardcore guy that wants to blow the the main storyline ASAP and not worry about all the side line quests and lore. For the casual player that wants to take their time, explore, and do all the quests, youll be able to get skills directly from quests. for the hardcore guy that blows through everything, you can get the minimum skills you need from skill trainers. Many skills you find on a skill trainer can be aquired through quests. There are some exceptions in both cases. Some skills can only be aquired by quests only, and some by skill trainers, and some ONLY by capturing them from monsters.
Skills and class are an essential part of the game. While many here have been comparing this game to Diablo 2, this is simply not the case. Asherons Call 2 was more like Diablo 2 with the skill system. Diablo 2 has skill "trees" where you automatically get a skill after purchasing the previous one. There were also a limited number of skills in the first place per tree with many skills being utterly worthless. As such, almost every character had a choice of 2 or 3 builds and as such everyone ended up as clones of each other.
The way skills work in Guildwars is there is no trees. You Pick a primary class AND a secondary class (which can be changed later in the game if you didn't like your original secondary class). Each "class" has a total of 60+ skills to learn. There is no pre-requisite for any skill other then the fact you have to FIND it. Nothing in this game is automatic. If you want the Sprint skill for a warrior character then you either find the guy that gives the quest with the sprint skill as a reward, find a skill trainer willing to "sell" the skill to you, or capture it off a monster if you purchased the capture signet skill off a skill trainer.
However, despite the overwhelming amount of skills, you can only have 8 active skills at anyone time. You can also only choose those skills in town. Once you are in a dungeon or on a mission, what you have chosen in town is locked intoplace until you return to town. Returning to town also resets any mission you were currently on if you haven't completed it. Many skill in this game are highly useful with many working GREAT in combonation with others. However, you can't have it all so you must choose wisely.
Now, for the RPG or story part of this game. I must say after FINALLY finishing it, the story was downright AWSOME. Many, many, MANY plot twists and character development. I don't want to spoil anything because it is just that good. With the promise of FREE story updates later and purchaseable expansion packs.. this game just keeps looking better and better for the purchase value. You get a great game, with excellent replay value, and many different forms of gameplay to chose from. PvP, to PVE questing, to Item hunting, to merchanting and hawking wares in Lions arch and basically having some fun with actual "role-playing". Heck, I rarely find an instance where I don't see a group of people screwing around with emotes with each other.
For those that REALLY want to solo this game from start to finish, I will say it's doable. I've done it. You just pick up henchmen to fill in spots. I actually LIKE the henchmen because, while they aren't the brightest, they can be controlled and their AI, like all AI is predictable. While they aren't usually as "powerful" as a regular player character, they are at least reliable. There is different ways you fight with henchmen then how you would fight with other player characters. Learning how to do called shots quickly by holding down the CTRL key and pressing the spacebar for automatic action after Tabbing to select a target is KEY to using henchmen correctly. Some people will argue that some missions are impossible with henchmen only, but that is incorrect. I have literally done every quest in the game with henchmen only right now. The key is changing your play style to suit either henchmen or player characters.
I've done every quest with players too. The mission in this game do get very difficult later on, and some seem REALLY difficult, if you don't use your brain sometimes. For example, I was on a mission where I had to capture a "keep" and then defend it from a seige of enemies. My team originally just tried to rush out and kill them directly. It didn't work. Too many enemies to fight off. I redid the mission with another team and this time we used the tools in the mission that we were meant to use. Mainly the Balista laying around. Using them and waitng for the monsters to get into the target area and smashing them with the balistas made the entire mission a cake walk. That's just ONE example of a mission having multiple ways to be completed. Sometimes you take the left path and sometimes the right. Either will get you to the end but one may be short and hard and the other long and easy. Ring of Fire is a good exmaple of that.
The only downside to this game is the fact there is NO offline play. Other then that, the graphics, music, story, gameplay, features, strategy, pvp, and everything else is done damn near perfectly. You get the feel of an MMORPG in some cities without the hassle of everything bad that MMORPGs have (aka kill stealing, camping, trains, blah blah blah). The replay value of this game is immense for those looking to maximize their characters for th PVP aspect of the game.
The best aspect of this game is NO MONTHLY FEE.