I liked Die Hard 4. It was fun and yes, a little stupid, but I was entertained by it. I don't care what other people think.
Of course it was entertaining and fun. The point was, it continues on from a series that started from a movie that is considered by many to be one of the greatest action movies ever. The first movie had good characters, tense and claustrophobic scenario, smart action sequences, good plot progression, a great climax, some extremely tense scenes, a great thrill and tension that went through the whole movie and a great way to finish the whole thing off.
It's not a question of whether DH4 was a bad movie, it's more of a question of how it supported the series, and I personally, being the die hard Die Hard fan I am (couldn't resist, sorry), felt it brought the series down and didn't live up to the high standard that was set.
Then again, I felt the same way about Die Hard 3.