dadofsix, I'll try to explain the differences as I know them, but others here may know much more than I.
OD's picture comparison is a good starting point.
The first thing you notice is the differences in the slide. ENH has forward slanting cocking serrations and a shoulder cut 'flat top'. The slide is the same external dimension but the shoulder cut is at a tighter radius than the Non-ENH slides(if that makes sense).
There's a slight undercut under the trigger guard, a different style hammer and trigger. I don't think any of the internal parts are different.
From what I have discovered over the years is that the ENH pistols are not very popular. I venture to guess it's because of the 'flat top' slide. It's a different look. Some like it, others say it's not a traditional look.
From what I can determine, the ENH version came out just before the XS version. Then came the XSE. Sort of a progression of styling from Colt.
For a lot of folks, including myself, these styling changes were unsuccessful attempts at garnering market share. The latest incarnation, the XSE, is I believe the nicest looking of the line. I have a Government XSE and I suspect I'll get a Commander XSE when I run across one. It's hard to stop buying them!
