Best Guild Wars yet, but still not flawless
The gameplay is not substantially different from the last two. The new spells and classes will surely broaden the spectrum of the PvP realm, although the classes don't seem to be as fundamental as the core 6. Same thing with factions, although the game doesnt seem to suffer as much from the new classes. There is definitely a Dervish overpopulation in Elona right now, but they are actually an asset to a PvE team, unlike (usually) the assassins in Factions. The hero battles are fun, but don't compare to the PvP types allready implemented thus far. However, the hero system (the "major" innovation in this) I believe is doing more harm than good, since many people simply use NPC's through the campaign. It is by no means hard to find groups, but you will encounter less full groups of humans.
The graphics are significantly improved over the previous games, although the effects may be subtle. They added numerous shader technologies, such as environmental lighting, some bump mapping, and better bloom and distortion effects. Also, the environments are alot more detailed, especially the amount of vegetation. The world is beautiful, and varied enough to keep things interesting. The later areas in the game simply look hellish and the creature designs range from generic (more insect enemies) to awesome hellish demons.
The sound is good, but not fantastic. The music and sound effects equip the game very well, however there are no songs in this game that I imagine people will be humming in their heads or listening to for leisure listening. The sound effects are great; they have a powerful sound to them which brings a intense adrenaline packed feel to the combat. Some of the enemy roars will even surprise you if you aren't paying attention, and sound downright scary.
The high point of this game for people who allready own previous titles would definitely be the campaign. The story is amazing, unlike the previous two installments. The campaign is extremely fun to play through, and takes quite a while (40-50 hours). The campaign in this game is as fun as many single player rpg's, if not better. I cannot stress how much better the content and story of this game is than the previous two. If you do not own Guild Wars or Factions, then the only thing that should stop you from buying this is if you don't have the cash, because not only will you get an amazing campaign and world packed with content, but you will have access to the shared PvP content of the previous titles, which is even more amazing than the campaign (and highly competetive).