If you want to say "это был вкусный", you have to point out what exactly was delicious. For example: "Это был вкусный обед" Or just "это было вкусно" Does it make sense to you, John?

John, honestly I don't know. I'll give try to give a verbose grammatical desctiption of my confusion... Perhaps someone else's shorter answer will prove to be more helpful:) Russian -о words are tricky in terms of part-of-speech classification. Perhaps their 'protorypical' meaning is - "short form of a neuter adjective". Это пальто слишком дорого. "this coat is too expensive", coat is neuter. But they also can be - adverbs (быстро идти, to walk fast), also they can be - a part of speech that was introduced by some linguists only a few decades ago, one incorporating "it", as in "сегодня солнечно" "it is sunny today", "вчера было тепло" "it was warm yesterday". What is English "it" here? It refers to nothign specific. Just it. - some other very exotic things, sometimes even nouns. E.g. "тепло" 'warmth'. and borders between these parts of speech are unclear sometimes. Consider also: "Мне хорошо", "Мне тепло" "I feel good", "I feel warm". If we take "тепло" to mean "it's warm" (like in "it's sunny"), then literally Russian 'I feel warm' is "to-me it-s-warm" We can try to interpret you "было вкусно" the same way: "[it] was tasty", "[it felt] tasty".

Вкусный суп | салат | чай (муж. род) Вкусная каша | рыба | конфета (жен. род) Вкусное мясо | рагу (ср. род) Вкусные пельмени | вареники (мн. число) Если же нет уточнение, что конкретно вам понравилось, а даётся общая оценка, то просто "Это было вкусно"

It's quite simple вкусно and вкусный are different parts of speech: & Вкусно is an adverb for delicious. We use the word "как" (ENG: HOW) for adverbs to ask the question & Вкусный is an adjective for delicious. We use the word "какoй/какая/какие" (ENG: HOW) for adjectives to ask the question. As you see in Russian depending on parts of speech we use different question words for HOW. Saying "это было вкусно" you literally answer the question "HOW was it?" (RUS: КАК это было? so they want to hear an adjective as an answer), which is usually asked differently like "Тебе понравилось?" (ENG: Did you like it?) or "как тебе?" or "тебе было вкусно?" - Saying "это был вкусный... (ужин/завтрак/etc)" you answer the question "HOW was the (dinner/breakfast/etc.)?" (RUS КАКИМ был обед/завтрак/etc ? so they want to hear an adjective in your answer). Such question can be asked in some specific situation where your detailed evaluation or comparison of different meals or places are necessary. It's like the question "How are you?" in English culture. Therefore just answer simply with the use of any appropriate adverb (было вкусно/посредственно/отвратительно/изумительно/необыкновенно).

Hey, John! The point is that we use an adverb next to a verb if there isn't any noun: быть + adverb Это было вкусно/хорошо/плохо etc. But if there is a noun you want to describe, use an adjective then: быть + adjective + noun Это был вкусный обед/это была ужасная вечеринка/это были чудесные выходные etc. Hope this helps!