The problem with priests is not that they are powerful but that they can replace other classes...
Domains should make a bigger difference. There should be a list of gods with predefined major and minor domains (one list for oc and custom lists for modules). The god selection should make a priest be REALLY different.
If each priest would have a limited set of spells closer to his god domains they would stop being ultra-flexible-do-it-all and have more character (OMFG this is the fire priest who can put me on fire!). Also, most players cast only 5-6 different spells anyways... They would be more limited but still happier overall because they would be different!