Go on - you know you want to!
My only real downer about the game is that the new characters are not playable through the original role playing saga, which would have added a new twist. Hopefully, Guild Wars 2 (when it's finally released) will solve the issue. In the meantime, this is a great game to get in to.
I'd suggest that you download the game from the Guild Wars website and pay for the "tripple play" version (currently about £20) and avoid anything on eBay. There are people selling the DVD Rom that is simply a copy of the downloadable content with the 14 day trial code that you can get for free from Guild Wars. Once you've paid for the game, there are no further fees to pay.