It's not as bad as people are making it out to be, but it isn't great either. A big issue is their admitted target audience was younger teen (tweenie) girls. Which is an odd target audience for a zombie apocalypse but hey it could have worked, but it didn't. So if you love watching teenage drama shows, Twilight and the such, you might love it! But it does get a little old for adults that really want a bit more substance to the writing.
Also as an adult there were multiple times I watched where the zero's were just doing nothing while the main character fought one off, or there are several on the car, but they don't attack they just sit there while they decide to drive off. Or another time they are running down a hallway and they are relentless climbing over each other and at a dead run, but when they catch up to the main character, suddenly they are slow and lethargic so she can fight them 1 or 2 at a time. There was an actual scene where a small horde is chasing her and crashing through doors and nothing seems to be able to stop their dead run but once they catch up, the rest literally stood looking in other directions in the fuzzy background while she fought one of them on the ground. They waited patiently until they were done and then growled at her as she backed away in terror and then stood up and then ran away. That was seriously some bad choreography, but it didn't ruin the series for me, it still had very good elements.
The acting also wasn't that bad. A couple characters were actually really good such as the fat guy (can't remember his name offhand) who was cleverly written to be a badass but also comic relief in a way and Evelyn was pretty good. So was the older Jade who was decent.