The Undead plays out a lot like the aforementioned 48 Weeks Later, with rival gangs needing to come together to escape hordes of zombies. However, while still not being amazing The Undead is a much better executed movie.
While obviously made on a shoestring budget nothing feels cheaply created. The makers have clearly seen their financial limitations and not been overly ambitious which I feel makes for a better film. All the effects are physical rather than relying on CGI.