hmm well, i came from Asheron's Call 2 to GW. I enjoy(ed) both immensely, but they ARE quite different games. (please note that i didn't play AC1, if that's what you are asking then my apologies as this long reply won't be very applicable.)
but, this is going to be my personal reply (in 2 parts!) I guess, as a current GW player, and with AC2 still fresh in my mind. More of a comparative review, maybe, to whoever finds it useful. Feel free to disagree with anything I write.
1)Graphics
both games are a feast for the eyes, one must also consider that AC2 is a couple years old now and its graphics are still very competitive with other games. I used to love just running around the world, or running up to characters, zooming in and admiring the texture work that the AC2 artists put in. That said, Guild Wars blew me away with its graphics during the open October beta, and I loved it since then. Guild Wars' world feels so much more detailed and immersive, while AC2 tends to re-use mobs and landscape and dungeon textures (small dev team.. i know.) the Empyreans didn't impress me in the least, it looks like their art team just took a human model and stretched it out a little... sigh. The other characters and their movements, though, are very well done and animated, particularly the Tumerok race (ok so I might be biased toward them.

) In fact, it's the humans in AC2 that are lacking, and the original races that shine. In Guild Wars, the characters are gorgeous, the world feels like a world, saturated rich colours, extremely detailed... but of course, Guild Wars is quite a lot more recent and with a lot more artists on its team, and a LOT more possibilities.

While it pains me to say this, but AC2 will never have the diversity of graphics, armour, environments, etc, that Guild Wars has already and is expanding upon. (i do wish, though, that people with a video card that can handle it, could turn on the option to see everyone else's armour textures and such at full res, not just your own. I love to look at the little details like armour designs. )
2) Gameplay:
Guild Wars is a pleasure to level in, you can log on, gain a few levels, log off feeling like you have accomplished something. In comparison, AC2 is a huge grind, yes. But it has become much better than it was when I first started playing it 2 years ago. Heck, I remember leveling my first character, the dreaded lvl30s were nearly empty of content and consisted of getting together in groups, going into the frozen Linvak wastelands, and killing either large goats swinging axes, or shreths and armoredillos. Repeatedly. :P Now, they have added a lot more content and quests. Though many of these ARE either "kill quests" or "fed-ex quests"... which Guild Wars has, also. However, Guild Wars has very epic missions just about every other town, and the kill quests and fed-ex quests feel like just little side quests, a pleasant surprise of XP or a skill or two. Guild Wars' strength in questing, IMHO, lies in the story-driven missions. It leads you through the world and tells the story, with all its wonders and treachery and honour and victories. And Guild Wars does it very well. AC2 tried that with the Vaults, and I enjoyed those, there was a new one with a new bit of lore just about every other level... until 50. Now, I have not played the AC2 expansion pack, so there may be new content for lvl60s and above, but I am no authority on that. AC2 does have its epic quests where many people are needed, and there are some for which literally half the server shows up. I sometimes wish that I could see that many people all working toward one goal, in Guild Wars, but alas, GW fellowships don't go above a set number of people (8?), and that's as many as can go into an instance. So, there is the feeling of "epic" through the story and environments, but less so through sheer number of people participating and fighting together against one common foe... (and in AC2, same one, once every week...)
(to be continued)