I can't disagree with SKR more. Mechanical benefits are one thing, and not covered fully either, but flavor is a huge aspect of any character I (and many fellow gamers) play.
There's also the 'burst' weapon enhancements which make criticals all the more important.
Imagine a flaming burst, shocking burst, keen rapier with Improved Critical stacking. On a critical hit you're talking an additional 2d10 on top of normal critical hit damage. That's a minimum 40% of all hits if your local cleric blessed the group.