The original might be worth more of your time, but the new classes are nice.
Game play hasn't advanced much from Guild Wars. The enemies have gotten stronger earlier on, you level faster and you find it hard to get into a party for missions because of your distinct class choice (if you want an easy time, go for a Monk or Warrior for more party invites. Necromancers also get an easier time than the others.) I won't go into detail about the 8 classes, but I'll say their main ability track.
Warrior: Fighting.
Elementalist: Your standard Black Mage.
Necromancer: Minion Summoning magic, health draining magic and curses, or hexes if you will.
Mesmer: Hex master. Literally.
Monk: Your standard White Mage.
Ranger: Your archer and pet master.
Assassin (Factions Only): Another fighter, weaker in defense and better in speed.
Ritualist: Your standard Summoner with a huge handicap (spirits never move, no elements, which I find lowers their appeal).
This game is mainly attack enemies and track through the many paths to gather treasure and gather lots of money. The game doesn't start until you get good armour and a good set of weapons, and level 18-20 (literally, it starts at 1, but all the good stuff is at 20.)
Graphics are the same as Guild Wars, and there is loads of room for improvement, but this is what I would expect from a non-profit company (by non-profit, I mean no monthly fees to play this game.)
Sound is very Oriental in Factions, which suits the Asian setting perfectly in my view. It can get annoying to certain people, but it may also appeal. Not much to write home about, as I can't pinpoint too many tracks in the game, but it's ok.
Overall, this expansion pack is NOT worth the $100 (or $50, depending on where you live, whatever. I haven't checked any recent prices.), but if you don't own the original Guild Wars, you can play this, as it is stand-alone OR an add-on pack. It's better to mix your original Guild Wars and Factions accounts for both continents to be open for exploring.
You might want to wait until it goes down in price before actually buying this. It is heavy on PvP content, but you need to be in a real Guild verse Guild guild or a good PvP or Heroes Ascent team/guild.