"That game is expensive."

Translation: 那个游戏很贵。

[Andrew-Lin]

那個遊戲很貴。

[samtullivan]

那个游戏贵。should be an acceptable answer. The question didn't say it was very expensive, just expensive.

[Andrew-Lin]

This is very unnatural. Nobody just say "贵" without "很".
Actually we seldom use adjectives without any adverbs. This is an interesting difference between Chinese and other languages.

[AJWentworth]

Yes, I thought the same. On the other hand, having taken lessons from a native Mandarin-speaking teacher many years ago, I cannot recall her ever saying that anything was simply "贵". If things were expensive, they were always "很贵".