Guild Wars can be best described as a cross between the real-time action of a game like WarCraft 3 and Diablo with a framework of player customizability in the vein of Magic: The Gathering.
In a nutshell, a real-time, action-oriented, monster bashing, online multiplayer version of Magic: The Gathering.
Unlike most fantasy role-playing games that has your character "naturally" gradually increasing in power from a farm boy to a superhuman being capable of levelling cities, Guild Wars instead relies on player skill.
You must selectively choose the skills (spells/abilities/special attacks) that you want to use at any given time (like choosing your cards in a game like Magic: The Gathering or Pokemon/Yu-Gi-Oh). Your collection of skills is much larger than the ones you can bring with you into adventures, which means there is skill in choosing the right skills.
Then, when playing the game, you must be skilled in actually using the skills (!) you chose... again, very much like a trading card game... you have to know how to use what's in your deck. Add to that the real-time strategy reaction skills needed to be good in those kinds of games.
Guild Wars isn't a hard game, but it has an incredible amount of depth. If you like games that have some "meat" to them, and that is challenging to get really good at, then Guild Wars is the kind of game you would like.
Regarding magic... it is a major focus in the game. And the game includes gods and demons and fantasy monsters. One of the character professions is that of the Necromancer, which deals with death and corpses and hints of vampirism and such. Elementalists wield magic that controls the elements of fire, air, and water. Rangers and Ritualists deal with the spirit realm, including "binding" spirits to do their will. The only non-magic/non-spiritual professions are the Warrior and Assassin.
Also, this is a "fantasy role playing game", so is very violent (not gory, but nearly 100% combat). The whole "point" of the game is to kill things (and other player characters)... just like 100% of the fantasy role-playing games out there.
If these things are objectionable to you, and feel they would hinder your spiritual life, then it might be best avoided.