That's pretty much how I feel. I liked 1 and 2, they were "Die Hard", but 3 and 4 felt like generic action movies with some action sequences strung together.
Die Hard is an accidental franchise. None of the movies, including the first one, started out as "Die Hard."
Die Hard was based on a book called Nothing Lasts Forever. The main character was Joe Leland, he was there to visit his daughter and she dies at the end. Wiki says the movie followed the book closely but I disagree. Aside from the basic plot there were significant differences.
It actually started out as a sequel to Commando, with Arnie rescuing his daughter again, who doesn't die. The stories were similar enough that Fox bought the rights to the book to cover themselves. Then Arnie dropped out, and it was no longer going to be a Commando sequel, so they started thinking about incorporating some bits and bobs from the book, and changing the lead character from invincible Arnie to a more vulnerable everyman.
On a scary note, the book is actually a sequel to The Detective, which was filmed in the late 60s with Frank Sinatra in the lead role - he's the original John McClane, in a way!
Die Hard 3 started out as a Brandon Lee action movie called Simon Says.
Which was originally optioned as Lethal Weapon 3 - hence the buddy dynamic in it...