The power increase is modest (usually one minor combat ability and something defensive/miscellaneous). The war and strength domain abilities are nerfed somewhat so it's pretty tough to make a cleric that can do serious melee damage and it's impossible to make one that outshines the fighter/paladin/barbarian. The lack of heavy armour and that they didn't benefit from the HP inflation that some other classes get means the cleric is weaker in combat compared to other PF classes than the similar comparison for the 3.x cleric. Most of their power inflation is in making the class fun to play (channel healing) rather than more powerful in a DPR or battlefield control sense.
The full spell list is archetypal for the D&D cleric but with not much for direct damage and most of the non-summoning control spells being a level later than the same for wizards, their list is inferior well into the middle levels at least (9th in my home campaign).
Despite being run pretty well, the cleric in my group is a contributor and always has lots to do but he doesn't rise above the pack, can't come anywhere near to out damaging the glass cannon archer ranger or the really hard to hit sword and board fighter.