You know the Romero formula- unlike the old Voodoo Zombie movies, his ghouls are more like a plague of some sort- a public health crisis. Here, there's an island filled with humans and the hope of security. Alas, humans always fuck it up for themselves in Romero's films. In this case, two warring families with an age-old grudge can't agree on whether to shoot all the living dead in the heads or keep them around and try to live with them. All hell breaks loose in the last reel, as it always does in these movies.
Romero injects social criticism into most of his movies, and in Survival of the Dead, he's depicting the small minds of small towns and their endless grudges. For me, Romero is best when his critiques come in the form of parables- as in Survival of the Dead or his earlier Season of the Witch- than they do when he takes an action story and tries to shoehorn in commentary- as in Diary of the Dead. Because he's working in the parable mode in Survival, he can develop a fully fleshed-out story with compelling characters. Even though his dialogue is still clunky, this movie feels literary, or at least Stephen King level literary.
So there are compelling characters, a darkly funny parable, and plenty of zombies being shot in the head or eating each other. It's nothing great- and not really on the level of Dawn of the Dead- but, seriously, it's enough for me!
*(There were zombie films before Night, but Romero updated the concept greatly by treating the zombies as a public health issue/outbreak scenario; just like he updated vampires with Martin and witches with Season of the Witch. In this case, everyone has ripped of Night of the Living Dead.)
Postscript: One criticism- directors, please stop with all the CG- it looks fake and cartoony.