The problem with the two-handed archetype is that you give up Armor training. This reduces your mobility, unless you go for a mithrill breastplate (this will, of course, reduce your AC). Fast enemies will outrun you and archers/casters will be a nightmare. The only thing you get in return is a little more damage for your iterative attacks and a cool ability at 15th level.
As for Critical treat... it is my understanding that 15-20 is as low as you can go, with an 18-20 weapon and Improved Critical. If I am mistaken, please point it out!
The Critical feat that works the best is the one that Stuns. Remember, kids! A stunned opponent drops all held items and looses a turn!