Die Hard is OSR
"The more of the following a campaign has, the more old school it is." - Principia Apocrypha.
1. Concrete Spaces
In Die Hard, Nakatomi Plaza is a fabulous dungeon. It is jacquaysed to all hell - elevator shafts, hidden ducts, and interconnected floors - and everyone involved takes advantage of this. McClane sneaks around like a rat in a maze.
2. Blorb
When the GM is asked "is there an X here?", they say yes according to what is prepped about the building. However, key elements are set - the C4 under the rooftop, the qualities of the safe, and the security systems. This balance is struck deliciously to be used to maximum effect by both protagonists and opposing forces.
3. Tactical Infinity
Weapons can be stolen. Glass walls can be shot. Rulings on the impacts of bare feet on movement speed can be made. The affordances of a building that is partially under construction are available to all agents in the scenario.
4. Factions and a Living World
The Nakatomi Corporation, the LAPD, and the FBI all have roles to play in the situation faced by the players here. They have competing interests (and jurisdictions) and star NPCs, but these NPCs don't steal the show overmuch from the player characters.
5. Social Play Without Rolls
Gruber is able to figure out, just from context clues and observing what the GM has placed in the room, who is related to whom and who is lying. He is not doing anything supernatural or relying on raw charisma - he is observing, using what he sees, and adapting accordingly. This is player skill!
6. Planning is Rewarded
The players clearly did their homework on the building, being able to take advantage of the FBI's standard responses and use the environment to their advantage. The GM allows things to succeed when the plan merits it.
7. Lethality
Guns kill people - in explosive '80s fashion, but they still kill people. And, when hirelings are killed, backup ones from the stable are recruited to become star players, in grand troupe-play fashion.
Also, fall damage.
8. Lack of Encounter Balance
McClane survives an indefinite amount of HP loss and hits far above his weight class. The PCs are threatened by him not because of his stats, though, but by his planning, which is fairly run by the GM.
9. Impartial Arbiter
When a plan fails, a plan fails. See above re: fall damage.
In Conclusion
Die Hard is an impeccably-run OSR heist adventure. It's a shame the player characters did not get to walk away with the treasure, though.