I have my Defiler to lvl 28 now, and I am having a blast with him. There is much more to a defiler than just healing/warding. They have a plethra of things they can do. Including dots. At my lvl, with 2 combined dots, I am doing 100pts of dmg per tic. Of course you still have to ward/heal, but there is much to do as a defiler. Much fun imo.