I have not yet begun to actually playtest Pathfinder (having just discovered it yesterday), but as I page through the classes section I'm finding myself simultaneously pleased and unnerved with the revised base classes. For the most part, I'm loving the redesign. However, there was one particularly worrisome ability I saw when I came over to the Fighter. The ability in question is the Pathfinder Fighter's capstone ability, Weapon Mastery.
Now, with the stated purpose that Pathfinder is meant to bring Core in line with splatbook material, I hold no bars here - Weapon Mastery is far too powerful as written. The only comparable ability that I could find was the Blessed weapon property from MIC (and the bless weapon spell from the PHB), and Blessed only works 3/day and only against evil enemies and does not operate in conjunction with any other crit-related abilities or effects; the bless weapon spell similarly functions only against evil creatures and not in conjunction with other crit-related abilities. So, as written, Weapon Mastery is already superior in every way to these powerful but strictly limited abilities.
Coupled with the increased critical hit multiplier, Weapon Mastery just seems excessive. Not only do you auto-confirm on everything, but you also do more damage when you do so. If my group elects to switch to Pathfinder, I'm already going to be nerfing Weapon Mastery. So, how about this - what if Weapon Mastery instead simply gave the increased critical multiplier? A nice ability, but not as insanely powerful as guaranteed critical hits that can be coupled with other critical abilities (unlike existing effects).