I kinda like it. Not only for the nastier-but-rarer-crits, but for getting "averag-er" results. That adds more weight on the skill modifiers.

what do I mean ? Well with two dice, there are more ways to roll an 11 then there are to roll a 3. Therefore 11 will come up more often (the closer to 10.5 you are the greater the odds). On a d20, the chance of any number is the same.

That means to pass a DC 15 skill check, you cant just put 1 point in the skill and succed 25% of the time, you will succeed much less. But on the other hand, the more skill you have the chance to succeed that check grows faster then with a d20 since the chances of rolling 2-5 are much lower with two d10.