The rap on the Series 80 has been the trigger, since Colt added the firing pin block. A lot of people don't like it, and they still prefer Series 70 pistols that didn't have the parts.

There's evidence, albeit not much, that the firing pin block is a definite safety feature; and there are a bunch of folks on the opposite side of the issue, that Colt folded under pressure from their legal department, changing a pistol with a good trigger, to one that was mushy and horrible.

A couple of years ago, Colt decided to bring out the Series 70 again, although they omitted the collet barrel bushing, which is what separates the pre-70 from the Series 70 pistols. They're enjoying a lot of success with the retro Series 70 GCNM.

I own both original Series 70 and Series 80 pistols, and I can't tell a whole lot of difference between the two.