There are tons of things to do with Guild Wars! You really need to complete one campaign to maximize your fun (and skills). Prophecies is probably the most long, drawn-out campaign, but still worth completing. Once you've finished, PvP is just one aspect. What else can you do?
-There are always weekend events to participate in. It gives you something else to focus your time on.
-Buy new skills and capture elite skills to make your character better.
-You can work on getting really cool armor and weapons. Upgrade them with runes and insignias to make you stronger. Dye makes them even cooler. Already upgraded yours? Now do you heroes! No heroes in prophecies though

-You can collect things: Mini pets, tonics, pets.
-You can work on titles, filling out quest books, etc. There are tons of side quests to work on.
-Zaishen quests/bounties, Nicholas the Traveler, War in Kyrta quests/bounties. They change all the time so you don't get bored.
-If you need money for the above stuff, you can find a place to farm items to earn gold. Guilds are really good for helping you to find something other than the storyline to work on.
-If you haven't found Wiki, it's a good place to research all of the above.
Have fun!!!