I needed to squint a bit to get full enjoyment out of this one for two reasons. First, since computers are a big part of the plot, I had to invoke the Cinematic Computer Rule: "Nothing you see a computer doing in the movies is possible." Being a computer guy myself, this does sometimes annoy me (such as the iPod in Transporter 2), but here, everything is at a fairly high-level - some guy taps on a computer for five seconds, and he's instantly tapped into a military communications circuit to a jet fighter. That kind of thing. Outlandish enough to just say "screw it" and move on.
Second, even though Die Hard is in the title, you kind of have to squint to make this into a Die Hard movie. Yeah, there's Bruce Willis running around, but he's not really acting much like John McClain here. He's relatively stoically running around, taking and giving out punishment. Not a lot of bantering, not a lot of improvisation, just moving from one set piece to the next. He really only comes close to letting loose in one scene, when he decides to "kill a helicopter with a car". And chief baddie Timothy Olyphant is certainly no Alan Rickman or Jeremy Irons - he's not even William Sadler.
So, the movie mainly suffers from the fact that it is a sequel to one of the best action films of all time. But if you ignore it (or at least downplay it), what you end up with is a competent action movie. As I said, it's pretty much plot setup, then set piece, move to next scene, set piece, etc. to the end. Many action scenes are just McClain in a shoot-out with one or two bad guys in a confined space (the goofiest of which occurs towards the end, against some kind of gymnast guy whose acrobatics get the worst of him). But there are a couple of scenes that stand out - Willis and bad gal Maggie Q trapped in an SUV suspended in an elevator shaft, and the world's worst Harrier pilot trying and failing to hit McClain in a semi-trailer on a highway mixmaster.
Another basic, turn-off-your-mind, reasonably good action movie. (Oh, and Die Hard 4.0 would have been a better title.) Three stars.