I thought the ABC version would be a weak BBC port. I was pleasantly suprised to see that I was wrong. The first few episodes of the American version are similar to the British version. Beating up suspects, rough interrogations, introduction to forensics and framing suspects... but they are their own shows and stand on their own well.
I think the BBC version is darker and creepier. The girl with the clown on the BBC sign-off screen weirds me out.