I'll tell you what impressed me the most about Guild Wars - The installation! I've never seen an online game that installed so smoothly (or quickly). The initial installer was tiny and within 3 minutes (admittedly, my cable connection is fast) the character generation was available and the client downloaded the Starter zone while I was making my first toon. I didn't have to wait at all to get in and start playing through the starter zone, and while I was doing so the client was busily downloading other areas of the world! Impressive
The graphics are very, very nice, especially if you can max out all of the effects like I did... I have a nice machine, but its not an uber-machine by any means (AMD 3200+, 1gb DDR400, Radeon 9800 pro 12

so I was pleansantly surprised by the quality and smoothness of the graphics engine. The models were nice (especially the chicks! YUM YUM), the landscapes detailed and engaging, and the animations smooth and believable.
I noticed a few brief moments of lag, but overall things were smooth and reliable... more good marks for a game in beta!
I really had no expectations as to what the game would be like since I haven't been following it at all, but I don't think I'll be buying it in retail.
Zones - For one thing it is restrictive... the zones, while appearing to be large, are actually just a series of cleverly disguised corridors that you cannot break out of. I don't know how many times I ran up against an invisible wall between myself an my objective... I found that frustrating. There were a few exceptions (a huge swamp outside of Lion's Arch comes to mind) and maybe this will change as more zones are added in the future *shrug*
Skill Slots - Only having the ability to carry eight skills into combat frustrated me as well. I recognize the "tactical" aspect that this brings to the game but I also forsee a huge problem with 'uber-templates' in this game... when you only have eight skill slots you can't get too creative!
Shopping/Crafting - I didn't care for the crafting / drop system, which seemed to drop cool items that were only for use as salvage items (as stated in the object's description). I did find a few weapons, but no usuable armor. This is something I'm sure will change, eventually

(or maybe I was just very unlucky?)
Missions - I thought it was an interesting idea and I did enjoy the mission I did (twice)... the one where you have to protect the cleric guy from surging hordes of undead. The henchmen were smart and useful (more so than the other players haha) and, if anything, made the mission too easy, but it was still fun enough to do twice
PVP - I didn't try it
Overall - While the game was fast paced and enjoyable it is just a little too simplistic to hold my interest for long. I had the same problem with Diablo... it was fun for a little while but once I figured it out there just wasn't much reason to keep playing.
It seems like a good game, but just not for me.