Questions & Answers about Что касается обслуживания, то оно нам всё же не понравилось.
Why is the word обслуживание in the genitive case (обслуживания)?
The verb касаться literally means "to touch" and always takes an object in the genitive case. The fixed phrase что касается ("as for" or "regarding") strictly follows this rule, so the topic you are shifting to must always be in the genitive.
Is the word то strictly necessary in the second half of the sentence?
Yes, in the Что касается ..., то ... construction, то is mandatory. It acts as a bridge introducing your main statement, somewhat like saying "As for the service, [well then] we still didn't like it."
Why do we need the pronoun оно right after the comma?
The pronoun оно refers back to the neuter noun обслуживание. In Russian, when you introduce a topic with что касается, you generally must use a pronoun in the second clause to grammatically attach that topic to the rest of the sentence.
What nuance does the phrase всё же add to the sentence?
It means "still", "nevertheless", or "all the same". It shows contrast or concession. Here, it implies that despite something else about the experience being positive (perhaps the food or the atmosphere), their opinion of the service remained negative.
As a quick refresher, why do we use the dative here instead of ?