Shadowmeld is probably most overpowered racial in game for World PVP and also instanced pvp, but the thing is shadowmeld doesnt work vs Demon Hunters cas they have stealth detection with 30sec cd.
And in arena if you will be facing Demon Hunters from enemy faction and your faction, they will simply reveal ur shadowmeld by attacking you with using stealth detection.
Still in World PVP Shadowmeld gives Nelf Gankers use advantage vs ppl who trying to Horde players who trying to kill Ganker, cas if you need AFK or alt+tab in areas where you cant fly you simple can run away to big distance and than shadowmeld behind tree or house.
Thats unfair, Blizzard should give nelves some good PVE racial simmiliar to Troll/Belf one, and give Engi profession item that gives "shadowmeld" for evry race outside rated pvp with 2min cd.