I love the puzzle element of GW1 missions. Can run them tons of different ways. There is also a strategy, a logic to it all. Just finishing up my new Mesmer in GW1 a few weeks ago. So that's like 10+ or so times I complete GW1. It was a blast. Even with shinier GW2 sitting on the same hard drive.
I've stated before that games with a heavy emphasis on action, twitch reactions and go-go-go combat are not my cup of tea. Though that isn't totally accurate because I can enjoy a quite few games [within reason] which go for that style. However, it's almost like GW2 went too far in the direction of "action" without the more cerebral elements I enjoyed originally.
The limited scope of what the gameplay can provide no doubt plays into that as well. Bandits attacking the town, centaurs attacking the town, kraka attacking the town, Skritt attacking the town... it's all the same mindlessness and repetition.
It's really like if you are not into PVP or Mario Bros. jumping, there isn't anything left but disengaging/afk farming. And I already did that to the point of no longer having anything to buy...