There's too much symbolism
I realize that this problem can largely be laid at the feet of George Romero, and I'll accept that, but every time I watch a Romero movie I feel like I'm being smashed in the face with the symbolism bat. It's not that he's an unskilled filmmaker -- although some have argued as much after seeing Diary of the Dead -- it's just that he's all-too-eager to use his zombies to advance whatever cause he wants to flog at the moment. Zombie movies are about ... racism. No, wait, zombie movies are about ... consumerism. No, no, the threat of nuclear war. Actually, go back to the first one -- they're about racism. Diary of the Dead, which I haven't seen, apparently uses zombies to set up the argument that there's too much reality TV. Has it come to that? I realize that zombies make a good catch-all, unlike, say, vampires, but there's a point where enough is enough. No more zombie message movies.
There's no growth in concept
No growth whatsoever, going back even before Bela Lugosi in 1932's White Zombie. One of the few interesting things about Resident Evil: Extinction was that it featured a subplot wherein the evil scientists try to reverse the zombie status of a zombie. They try to make him learn and regain some the cognition of a normal human -- but even this has been done before. Hell, the notion of zombies emerging from the fog of zombiedom has even been done by George Romero. What else have you got? The 28 Days Later films make zombies run fast and take care to not call them zombies, but that's hardly groundbreaking stuff either. Maybe the most innovative zombie movie I've seen in the last few years, Joe Dante's Homecoming, did something a little intriguing -- it gave the zombies a political motivation and had them intent on going to the voting booth. But even this is campy, and brushes up against my problems in point number one.