I've had these for a while and finally figured I'd post a review. I mostly run Castles & Crusades using my own homebrew setting and the Troll's default setting - Ahirde, along with their A-Series Modules (Assualt on Black Tooth Ridge, etc). C&C is my Fantasy Game of choice, and being OGL, I figured I'd give the Criticals (along with the fumble deck) Deck a try to see how it worked out. I run my game with a natural 20 being a critical and a natural 1 being a fumble. There is no confirming or threat. You roll it - it happens. In the past what this meant for a critical, was simply double damage (and for a fumble it meant you roll to see how much damage you do to yourself). Not very imaginative, but it got the job done. Well, this deck added a new dimension to the whole RPG experience for me and my players. Rather than simply double damage, now when a player or NPC rolls a Mr. Natural, the deck comes out and it becomes a fun event to see what will be drawn.
What Paizo has done is broken down each card into four differnt types of damage - Bludgeoning, Piercing, Slashing or Magic, based on what the character used to attack with. The one card I drew just now, interestingly enough, had Double damage for each type of damage but had additional effects such as Knockback, bleed, etc. The magic effect caused normal damage to the target but everyone adjecent to the target got hurt too. Anyway, pretty good stuff and everyone looks forward to drawing from the critical deck (and the fumble deck, especially when I as the CK roll a fumble for an NPC!).
As a C&C Player not all the stuff is applicable - Fortitude Saves, Conditions, etc. But those or easy to convert on the fly and haven't had any issues with theme in my games.
Anyway, well worth it for adding something bit different to your games.