Pros - great story with plenty of action and scares, fantastic acting, thoroughly convincing characters, each season better than the last.
Cons - not completely true to the books.
If you have not watched this show yet then I suggest you do. While on the one hand it may appear to be just an extended version of any other Zombie movie, it actually has far more brains and heart than most.
Beyond the scares and action lies a deeper story that, as the show progresses, starts to explore how the world copes in the face of a zombie apocalypse. It soon becomes clear that the walkers are not the only danger to Andrew Lincoln's humble sheriff, Rick Grimes, and his plucky band of survivors. One of the things that makes the show brilliant is that no character is safe and the creators are perfectly willing to make tough decisions with regards to plot development. It is this commitment to realism and grittiness that makes this far more than the simple cult hit that it might have been, extended it into the realms of genuine drama. This drama is supported by a cast whose acting is outstanding, devoid of weak links and settings that are scarily realistic.
If you are a fan of the original comics and are hoping for a carbon copy of that then you will be in for a few surprises as the show makes a number of changes. However, these changes are invariably for the best, not making it better as such, but making it more suitable for TV.
Overall, this is one of the best and most watchable shows of recent years.