IMO issue with the cleric are
1. the reliance on buffs and the fact that they can be interrupted, and when intervention goes off it rips all your buffs off you.
2. Weapon diversity.
This feels like the biggest hurdle in the game. There are hundreds of items in this game, and all most all of them are worthless on the cleric.
The list of two handed maces might as well be warrior only, none of them are as good as 1h-shield. You do less damage and take more.
IMO in nivarian or the temple one of the cleric skills should be reworked to be a two hand mace spec. with 10 str and a two hander i do less damge then with paladin sword, a lot less.
-or-
Add additional damage to the smiting skills, like +20 additional damage while using a two handed weapon.
Right now at 21 my cleric runs Precision strikes and Massive crits 3. Those two skills are so much better then spirit ward, death ward and retribution. It's not even close. Advanced skills need to be tweeked on the cleric really badly.
Battle prayer is good, but the rest are pretty bad, boarding on useless.
Why would I run resist buffs when I can just swap gear before I go to an area?
Why would I need to use skill points on an ability that restores mana when I can just potion?
I went the cleric guild so I don't have duel, but I have access to mana potions. If a new source of mana potions is dropped into the game then going the cleric route would be useless.
TL;DR
Buffs are fragil
Weapons are limited
advanced skills are bad
cleric guild needs a new better incentives for joining.
P.S.
I love the game, not complaining, those are just my opinions on the cleric. It's still a strong class