Critcal Expert

When you take this feat you may increase any ability score of your choice by 1.

You have become an expert at landing critical hits.  Your critical hit roll range is increased by 1.  if you would critical hit on a roll of 20, you also critical hit on rolls of 19.  If you have an ability that allows you to critical hit on a 20, or 19, you critical hit on an 18, 19 or 20 instead.  etc etc..