You have to be careful and if the crticism is constructive and not completely bashing the place you should be fine.
You'll find people screaming defamation for smallest thing, but read a copy of Timeout for example and not every review will be possitive, use your common sense and be a bit nicer than what you would be back home, if that make sense.
Is it legal to write a negative review on a blog, about a brand/company/service?
It is legal but you can also write a Facebook review on their page or google review
No, it is not legal, it is considered defamation! You can't write a negative review, restructure it in a way that you are asking for help then do hashtag and company on twitter or FB. Anything else you'll have to be careful with.
You are critiquing services specific to a company or brand directly on a website, so in essence you are promoting negativity about the company and its services potentially causing them loss of revenue, bad publicity, bad reputation etc.
Grey area in daily life but if someone takes offence you better be prepared to go to court.
Similarly, it is illegal to post about a person negatively.
Read the UAE Penal Code.
Is it legal to write a negative review on a blog, about a brand/company/service?
It is legal but you can also write a Facebook review on their page or google review