My suggestion is to find everything unique about Guild Wars and KEEP them.
In particular, one thing that makes Guild Wars unique is its emphasis on prevention. Monk's protection line, ranger and mesmer interrupts, knockdowns, etc. A lot of other MMOs clearly lack some of these mechanics, and others just ignore it all together. Making Guild Wars 2 "just another warriors + healers" game is one of the most damaging things they can do to the brand imo.
I hope others feel the same way I do. The idea of a mesmer or monk class is what makes guild wars unique. I've played a priest in WoW, I've played a cardinal in Lineage II. They simply do not compare to the monk in play. Guild Wars requires the player to be so much more ACTIVE, working to prevent and predict.