This is by all means an above average horror anthology. It has episodes that are stronger than others and some that fall too short but in comparison to many other horror anthologies it certainly stands above plenty.
Many judge this based on Zak and disregard the actual content of the episodes. There are some complaints to be held regarding cinematography, lighting, story and acting but both one by one and as a whole they have a common theme and feeling running through.
Don't go in expecting masterful horror, expect common themes and stories, some clichés but it has plenty of creepy moments while some episodes are genuinely great and creepy.
To comment on Zak, he is a persona that some don't click with. Personally I enjoy his antics with his team on Ghost Adventures even if ghosts don't exist, they have great chemistry while Zak individually has a perchant for being overly melodramatic and this can be argued here too.
All in all, I've enjoyed all episodes in some ways and some more than others. I'm in between a 6 and a 7, closer to a 7 than a 6 as I have enjoyed many of the episodes based on the horror element. As a series stacked up to others I'd say it's a solid 6.