Is this a good restaurant? - Ez egy jó étterem? / Egy jó étterem ez?
Is this the good restaurant? - Ez a jó étterem? / A jó étterem az?
Be careful with the word order.
(1) az étterem - the restaurant
(2) jó étterem - good restaurant
(3) a jó étterem - the good restaurant / egy jó étterem - a good restaurant
(4) Az étterem jó. / Jó az étterem - The restaurant is good.
(5) Az az étterem jó. / Jó az az étterem. - That restaurant is good.
(6) Az étterem. - That is a restaurant.
(7) Az egy jó étterem. / Egy jó étterem az. - That is a good restaurant.
(8) Az a jó étterem. / A jó étterem az! - That is the good restaurant.
Usually the article of a noun takes place IN FRONT of it (1), because they belong together in exactly this way.
The same rule counts for an adjective, which describes the quality of a noun. It always takes place before the noun. (2)
Now, if the article and an adjective appear together and "battle" about the place in front of the noun, the adjective wins (3) and the article is place before the adjective. The article might change (a <=> az) because its form depends on the beginning of the next following word.
Putting the adjective behind the noun or in front of the article changes the meaning, the adjective becomes part of the predicate (4).
Combining a noun with a demonstrative pronoun (ez/az) for saying "this (one) /that (one)", you have to use an article between the pronoun and the noun (5). Without the article it gets another meaning (6).
I hope, the last two sentences explain themselves and my words were not bedazzling you :-)
"Is this a good restaurant?" is not the same as "Is this restaurant good?". In the first sentence "this" could be anything - even a car, and you want clarification that the thing it is is a "good restaurant". In the second the subject of the sentences is "this restaurant" and you want to know its quality.
But we are already talking about "this restaurant"... your sentence only implies we are not dumb to mistake a restaurant for something else.
And I can only talk for Hungarian but I feel like "Jó ez az étterem?" is a question one could ask while having a meal there while "Ez egy jó étterem?" would be pretty awkward.
"Is this restaurant good?" is asking about this restaurant. We know it is a restaurant - but what kind? "Is it a good restaurant" is asking what is it? Yes, it can be taken as the same - but it also is not assuming "it" is a restaurant. It could actually be a hotel or a menswear shop.
Your answer asks about something (possibly a restaurant - but not specifically), the Hungarian ask about a defined thing "this restaurant".