As a general rule of thumb, your average CTR for an adgroup or campaign should be at least 5%. If it is below 5%, you've got work to do.
Your CTR doesn't really depend on the market you´re in. It depends much more on the way you set up your campaigns. We´re pretty much always reaching values between 5 and 10% at adgroup and campaign levels. For individual keywords the variations are much bigger of course.