I quite liked 4.0 (despite the lousy title) and it's better than 2 (Die Harder always seemed too much of an in-joke.) But Die Hard with a Vengence is still the second best film , 4.0 has a better ending, but Vengence has a better overall plot and, most importantly, a damn fine villain.
The original is still the best by a country mile though, and will remain probably the best action film ever made, IMO of course. The big difference between DH and 4.0 is one of believability. I'm not saying Die Hard was the most realistic film ever made, but seriously, pretty much everything McClane does is at least plausible. He isn't superman, he gets banged up something terrible and basically wins through by a combination of luck and stubborness.
Compare that to standing on a hovering F-35...
4.0 was a good action film without ever feeling like a Die Hard film.
If they make a 5th film I'd want the following...
* Bring back the swearing!
* Bring back Bonnie B, even if only in a cameo, even in the third still she was still a vital part of McClane's story.
* Bring back the claustrophobia. It was a wise move to go to a city in Vengence, but after the US under seige in 4.0 does anyone really want to see the entire planet get taken over by terrorists? Hell I'd be almost tempted to set it back in Nakatomi Plaza.
* Take more care with your villain. I like Olyphant and William Sadler, but neither had the scene chewing wonderfulness of Rickman or Irons.
*Cut out the cgi aeroplane dancing nonsense!
I doubt we'll get any of those fulfilled though unfortunately.