I actually liked Die Hard 4. Is it as good as the movies before? No, but I still thought it did a fairly good job in terms of how a modern Die Hard movie would look. I think people hate on it way too much, especially when Die Hard 5 was such a crapfest. The 5th one makes the 4th look like Citizen Kane. One of the most unexciting action movies I've ever seen. Bruce Willis looked like he wanted to take a nap through the whole film, and they didn't even try to make it exciting. "I guess i'm going to Russia now", and then quotes like "I got nothing better to do" and everyone just seemed bored.
The first one is still the best by far though. As much as I enjoy 2, 3 and 4, the original is the only one that I would call a masterpiece.