From what I have seen, it is mostly people who loved the game series and the other media it has spawned who hated the show. This becomes a lot like Judge Dredd here but Master Chief should never remove the helmet. That was a huge one for some. And the whole story of Master Chief being stolen and turned into a super soldier was never in anything before. So they basically threw away well established canon and made their own fan fiction. Folks tend to not care for that. But overall it seems to be rated at like 50-70% approval depending on the score so it isn't universally hated. Remember that those who are loudest are the most passionate and often are just being pains.