As Shadow Spirit said, it “depends on what your definition of "fun" is”.
Guild Wars now has 3 additional releases after the original Guild Wars: Prophecies. There are many threads about what is in each one, and the pros and cons about them. I would search them out if you are interested in getting back into the game, as they should be able to help you decide which GW expansion to purchase.
Overall, if you enjoyed getting your 6 characters up to 20th level in the original GW, enjoyed hunting for elite skills, and finishing up the story line after you hith 20th level, then you will very likely enjoy the other 3 releases.
If, on the other hand, you got to 20th level and were upset that your character didn’t get any additional health, or attribute points to “grow” him further, and you didn’t bother hunting down elite skills or playing out the finale of the PvE storyline with your character once you were 20th level, then you may not want to get back into GW.
Each new release has a new storyline to follow, with a lot of fun twists and turns. Also two of the new releases (Factions and Nightfall) each added 2 new Professions (Assassin & Ritualist, and Dervish & Paragon respectively) for you to make new characters with. Aside from making new characters, you can take your six 20th level characters over into the new campaign area’s and get new skills, and complete the majority (non-newbie areas) of the new story lines. In addition, two of the releases added Heroes (customizable henchmen) that you can take along with you.
The new releases did NOT: increase the level cap, increase the number of skills you can take with you, or imbalance the game by introducing uber-items that break the power curve introduced in the original GW. If this is a problem for you, then getting back into GW is not for you.
Also, I am not a PvP player, so I cannot comment on what changes were made from a PvP perspective – but I would imagine there are quite a lot.