I'm playing a high Cha/Wis Kalashatar Hospitaler, and the divine challenge effect is pretty fantastic. It's nearly impossible for enemies to hurt my allies if they ignore me, and entirely possible that they'll get healed instead. One skeleton last session attacked the sorcerer 4 times instead of me, and took 18 radiant damage for the trouble plus healed him for 40, dealing only 26 damage.
Even with the errata I'm still pretty happy (since it still triggers more than once a round). I've started to run into opponents who have the ability to get out of my mark and I'm sure I'll likewise start seeing more area attacks now, but all and all he's a very effective defender.
Basically I choose one target, and that target can not attack other party members for damage. Most of my powers are about hindering attacks or dealing with large groups (Astral Thunder, Hallowed Circle, Righteous Smite). He lacks some on the the mobility and threat that our two-weapon fighter was able to put on the bad guys, but on a whole he's very effective.