The first one, of course, was wonderful, and has earned itself a permanent place in cinema history.
The second one sucked balls. It was supposed to take place at Dulles Airport in Chantilly, VA, and they couldn't even bother to make it look like Dulles. The rapid swapping back-and-forth between live and blank ammo magazines was completely wrong. You need a blank adapter to allow the weapons to fully cycle, otherwise there isn't enough back-pressure to push the bolt back to load the next round, and if you fired a live round through it with the adapter still attached you'll blow the whole barrel off, if not explode the entire receiver into the user's face. The story was just kind of a formulaic re-hash of the original. With snow mobiles. Pfft...
The third one was quite good, IMO, with Jeremy Irons doing a fantastic job as Hans Gruber's East German baby bro. Samuel L. Jackson rounded out a very well-configured cast. A very good sequel to the original, following the traditional A/B/A trilogy pattern.
The 4th & 5th films were meh. I know I saw them but I found them entirely forgettable, as I don't really remember much about them at all. Lots of driving around in hazardous ways and big 'splosions. I think there were rumors of a sixth film at one time, but since I'm apparently not the only one that found 4 & 5 forgettable, and due to the failing health of Bruce Willis, I suspect it's all done, pending another franchise reboot down the line in another 5-10 years.