One of the greatest original MMOs in my opinion. Competing with EQ and WoW when it originally was released. Though it's nowhere near the content of WoW or other newer MMOs, it is still a great play, finding myself playing it every once in a while.
The game is primarily PvP based. Monetized tournaments and PvP based guilds are abundant and ArenaNet, in my opinion, really understood what players were looking for in PvP, and even more so in Guild Wars 2. No longer is gear a factor in PvP.
Even the storyline was rather fun to play and follow. If you enjoy game lore then you will sure get a lot of lore out of Guild Wars. Small in-game content and books cover most of the lore of the Guild Wars universe.
Due to being PvP based, many people have turned away from the game. I would suggest waiting for Guild Wars 2 to release within the next 1-2 years of writing this review rather than buying the original. But, if you really want to follow the storyline and even get a head start in GW2 by filling your 'Hall of Monuments' then go ahead and buy it. If you do, you can even ask me for help.
Even though I recommend this game, I still suggest you buy Guild Wars 2 rather than 1. Everyone will agree that 2 is a huge improvement over 1, though lacking some 1 content that we all loved.