I guess it depends what your expecting from the game and if you have played many MMORPG's before such as WOW and EQ2.
GuildWars isn't a MMORPG and doesn't claim to be. You can meet with lots of real life players in the city zones, but when you go out adventuring you can only take a small party with you as all the adventure zones are instanced. You can also do the actual 'Guild' battles against real people. I found this was fun, but soon got a little boring. I also found the levels themselves restricitive, it's difficult to explain but you come up against invisible barriers a lot, there are very distinctive 'corridors' for you to walk in which make it feel restrictive for me and really bug me for some reason.
I was initially very impressed with Guildwars, the graphics are great and the game seemed fun, after a couple of weeks the novelty wore off and I've never really gone back to it, I was soon back to EQ2 and WOW. I think I just prefer actual MMORPG's, I know plenty of other people who think it's a great game though.