GW vs WOW
I have played both GW and WoW extensively, and the main difference between the 2 is that in GW you can only see all players on your server when you are in towns,unles you are grouped with them. and in WoW if you leave the city you can still bump into other players in the environment. Almost all of GW is instanced. In wow rivers and oceans really exist, and you can jump in and swim. where in GW water doesn't go higher then your knees.
The PvP in WoW is a lot more intense, and can be both annoying and extremely satisfying, unlike in GW when you are out questing in WoW, players of the other faction can come along and wipe you out, which usually leads to you calling some friends and fighting back, and then they call more friends and a small war begins.
That is the biggest thing that I miss about WoW, I remember when I played a Tauren and me and a friend got about 100 Horde players together, we Hi-jacked the alliance boat we landed on the Night Elves Island and launched a full scale attack on their capital city. The battle lasted over 3 hours, and eventually we were forced to retreat.
That is something that you can only dream of in GW, but alas $15 a month became way to expensive, and WoW is way to addictive for me.