Improved Critical
It's just not as useful as you would think. At higher levels more and more of your opponents, Undead and Constructs, are immune to criticals. On average it doesn't do much more damage than Weapon Specialization, which has been mercifully culled. With two handed weapons, you're definitely better off with the Focus/Specialization/Greater Focus, for the Extra 4 points of Power Attack damage. Consistent damage is often better than an extra 5% chance of double or triple damage.
Plus you have to focus on one weapon. At higher levels, you never know what your next great weapon is going to be. Better to use Improved Init, Power Attack, Weapon Finesse, or feats that you get to use all the time.