Die Hard is definitely a must watch Christmas movie. In fact my husband and I watched it just before Christmas 2015. Although it's an action movie it's set at Christmas time and the final scene as he gets driven away in the car has one of the best Christmas songs to accompany it. We always watch it at Christmas time.
The movie of Die Hard is an action movie and although it takes place in the Christmas season, that shouldn't make it a Christmas movie. There are plenty of movies that focus on the Christmas season that should much be much higher on the Christmas movie list than Die Hard. Die Hard is a hardcore action flick that doesn't focus on Christmas or anything even close.
I haven't seen die hard so I don't really have an opinion on the movie. My favorite Christmas movie is the grinch because it teaches to always be kind, especially during the holiday season. It also teaches that no one wants to be around a grinch or a miserable person.
Why would Die Hard be considered a Christmas movie? Sure, it is worth seeing at least once, but Christmas has nothing to do with it. It's an action movie, not a holiday story or religious story. Anyone who watches movies because other people say they should needs to start thinking for themselves.