I kinda liked 4.0, despite the overuse of CGI, a terminally dull villain, and the F-35 scene. I think it just didn't really feel like a Die Hard film as such. I'm not a huge fan of 2, but it's undoubtedly a Die Hard film.
What I'd want from 5...
* A decent villain with personality. Is there another Gruber brother out there?
* Realistic action sequences (up to a point) the great thing about the first one is that there isn't much McClane does that someone wouldn't be able to do in that situation.