I have the original game and Eye of the North. I took my necro/mesmer about half-way through the expansion campaign. Every once in awhile I go back to it, but it's one of those games where I just don't understand all the little details enough to really get into it. I suck at PvP so I just spam buttons without really thinking about what I'm doing, and I have to follow along on the GW wiki in order to complete quests without getting lost or losing track of what I'm doing. (And even with a guide to follow it's still no guarantee that I'll finish it.)
I've played a lot of RPGs, but I think I got into GW waaaay too late to enjoy it fully. It's weird, I try to get into it but always end up confused reading forums about the game trying to figure out some sort of direction to take my character in.
Oh, and one really big thing that holds me back is that I don't own Nightfall or the other expansion, so a lot of the builds I read about I just can't do because I don't have access to the skills they need. I figure I'll pick up GW2 as soon as it comes out, though, because I did enjoy fumbling around in GW1 even if I didn't accomplish anything noteworthy.