Being an avid fan of the first one, I can safely say this one is a let down.
Factions is the semi-expansion to Guild Wars in which you get a new continent to go through along with two new playable classes as well as new weapons, new pvp etc. That's essentially the premise of the game. Factions is a personal let down for me, because Factions is basically Guild Wars all over again but with a rubbish story, setting and everything about the game. Once you've fully completed the first guild wars, you've seen everything these semi-expansions have to offer you. So, if you haven't played any guild wars games, go for the original it will be so much more worth it. If you have played the original guild wars, factions will be a good game to keep you occupied but please note it isn't as good as its predecessor and you may be let down. If not, you could simply wait for the first "Real" expansion; eyeofthenorth this fall.
Factions has a mediocre story to go with it compared to the original game, even by itself it doesn't bode well compared to any other game. The setting is dull, bland and repetitive and some of the co-op missions can be very frustrating and hard which is totally unnecessary when you're not even at the end-game. Some co-op missions take hours on end, to find out that the last boss of the mission is so hard you've wasted all your morning / afternoon for nothing. You raerely got this with the first guild wars considering the co-op missions were relatively short.
You have no sense of progression in factions either, by the time you've come out of the newbie island you're ALREADY level 20!!! So basically, by this point you feel that you have nothing more to achieve and you're merely wasting your time and your effort going through this game; and that's true. You do get nothing out of it and it does feel like you're wasting your time considering as most of the environments are unvaried and you're already at the maximum level.
The only praise I could give to this game is the theme of the game; i.e. some oriental continent. However, that premise in any game appeals to me anyway. It's not that well done in Factions and it doesn't suit the Guild Wars franchise.
So to summarise, Factions isn't the game everyone hypes it up to be. If you've played Guild Wars and you loved it, don't expect too much from Factions. If you're a Guild Wars virgin play the original. Factions is not that good of a game.