GW1 was an odd duck, since it was designed as "chapters" from the start.
Stand-alone Chapter 1, Prophecies, launched in April 2005.
Stand-alone Chapter 2, Factions, launched in April, 2006.
Stand-alone Chapter 3, Nightfall, launched in October, 2006.
The first of two Expansion packs, Eye of the North, launched August 2007.
The second of two Expansion packs, Bonus Mission Pack, launched November 2007.
There's also the Guild Wars Beyond content, but I don't know much about it. I think it's just free stuff to do, added in for people waiting for GW2.
You needed to own one of the three Chapters, to be able to play Eye of the North or BMP.
It's worth noting that Prophecies, Factions, and Nightfall can be finished in about a week each if you bolt through the campaign missions and ignore side-quests. Prophecies has 25 missions, Factions has 13, Nightfall has 20.
Realistically speaking, Guild Wars 2 has more story content than all three GW1 chapters combined, due to each race having their own missions, and variants on missions based on choices, etc. But of course, you have to make a character for each race if you want to experience it all, and it all tends to end up in the same place about midway.
However, the quality of GW1's missions far surpasses those in GW2. They were longer, harder (snerk), and generally quite more involved, multi-phased, and able to be played in a Hard mode for extra challenge. Though most did involve a lot of pointless walking from A to B and dealing with pop-up encounters.
Eye of the North being "end game" can take a bit longer, since it's more convoluted.