A nice crit mechanic

As a follow up to my last post, regarding critical hits. One thing that's neat with having to roll percentiles to hit is that you can have something cool happen when you get doubles, i.e. same number on both dice. Rolled over the target number and it's something no-so-cool and below something cool. At least in a roll low system. Almost worth considering even if you are using a d20. Just multiply by five and you can break out the percentiles. I first saw this in Top Secret/S.I. and I still love it.