Major improvements will make PvE solo players frustrated with the original very happy
The second installment (Factions) didnt change much if anything but it added a lot of new content.
Nightfall brings essential improvements that address almost all the issues this game had. Now the game is doable solo, a lot of depth added by the hero system.
This game will offer a very pleasant surprise to the players that quit the original Guild Wars because of its excessive difficulty and lack of solo play.