I've run two sessions and the dice gods have totally been with the GM. I can't tell you how many 20's I've rolled, at least 6 a session. I double-20ed once (which in my original D&D basic edition game was instant death) and crit'ed many times.
If the PCs didn't have the extra pathfinder HP (I'm using racial bonus HPs) at least half of the party would be dead.
The players are enjoying the additional survivability.