It's definitely worth it, I'll give u a little run down of whats happened so far !
Originally, there was the Human Kingdom of Ascalon, which was destroyed by the event called "The Searing" by the beasts known as The Charr (playable GW2 race). They and the Humans were enemies and shit, and fought loads before. The humans had some sort of edge before, but after using magic to destroy the "Great Wall" the Charr broke through, and killed hundreds. Then 2 years later, you continue the story, and after troubles in Ascalon, move to the Kingdom of Kryta where you encounter the White Mantle, who are the current "leaders" if you will, of Lion's Arch (Kryta's capital) and surrounding areas. When delivering the "Chosen" (who are later revealed to be sacrifices) the Shining Blade (bandits like Robin Hood) capture to Chosen to save them. Shit goes down, and you end up siding with the Shining Blade. You then meet a guy called Vizir Khilborn (something along those lines, can't remember directly) who you journey with kind of. You then encounter the "Mursaat" also known as Unseen, after a while, who are the White Mantle's blasphemous Gods, and the antagonists of Prophecies. You are "infused" to fight them, and then Vizier Khilborn reveals to be called "The Lich", an evil presence who threatens life on Tyria (the Magical world itself). You eventually kill The Lich, and retrieve an artifact called the Scepter of Orr, which he intended to use to open the Gate of Kamolie, which would release Titans upon the world to destroy it, which was his penultimate plan. This is all part of the "Flamekeeper Prophecies"
In a new land called Cantha (Still on Tyria, except across water) a plague breaks out. Soon to be revealed that the source is Shiro Tagachi, an Assassin who slew the Emperor years before, and was eventually struck down himself and cursed, trapping him for so many years. The curse ends, and he is released, releasing a plague, which corrupts and kills thousands within the city of Kaineng (Cantha's industrial land). You have to journey to Echovald Forest and The Jade Sea to retrieve artifacts from those who originally killed him, and stop Shiro. The artifacts however fail, and other means have to be found. Eventually, you stop the Luxons and the Kurzicks (Factions within Echovald and The Jade Sea) from warring, and they unite to kill Shiro. With the help of them both, along with the Dragon, Kuunavang, you slay Shiro, ending the plague (from spreading at least) and stopping turmoil in Cantha
In Elona, Varesh Ossa (the Leader of the Kournan armies) becomes corrupt. Varesh is a descendant of many Kournan heroes, who are legends in Elona, however Varesh herself dabbles in the Dark and Old Gods, and plans to release the "6th God" Abbaddon, upon the world, who was banished by the other 5 Gods. The heroes (you) Journey across Elona from Istani, to Kourna, to Vabbi and to the Torment realm itself to stop Varesh and Abbaddon. Eventually, you encounter Abbaddon after much difficulty, and slay him. The protaganist (Kormir, the Sunspear leader, who are the Istani guardians) replaces him as the 6th God, becoming the God of Truth, and restoring balance in the Realm of Torment.
Eye of the North
Eye of the North introduces new races, such as the Norn and Asura. It tells of how the Destroyers (later to be revealed the Dragon, Promidious' minions) rise from the ground to destroy the land above, under the command of the Dragon's, Promodious, General - The Great Destroyer. The races unite to strike down the destroyers, after later being against each other, and even the Charr and Humans become allies, with the character Gwen (a young girl from the searing 20 years on who has grown in fear and hate of the Charr) and Pyre Fierceshot becoming allies. The story of Guild Wars ends with the destruction of the Great Destroyer, and the restoration of balance in Tyria again.
Thats a little run down of the story. After that, over the next 250 years after Eye of the North - The dragons awaken, causing turmoil again. The idea is that "new heroes" being the descendants of their ancestors (the heroes we played before) have to rise up once again to fight off the dragons. It revolves around the uniting of the "Destiny's Edge" guild, which fell apart after failure, and caused divisions in the 5 races (Sylvari - the newest race, Asura, Norn, Human and Charr). It's a brilliant story, and waiting 5 years after it's announced has been fantastic. Can't wait for the release, and so happy to say GW1 was my first MMO, and that I'm still continuing the game today! I hope this helped you make ur decision, and gave u an idea of the lore etc. !