Is playing computer games an unwholesome activity?
There are different degrees of unwholesome activity. The term akusala (lit. unskillful, unwholesome) is a broad term that in addition to referring to 'bad' deeds (e.g. killing, stealing, adultery etc...) can refer to any kind of action that doesn't lead to the highest happiness. In this broader sense, all types of sensual indulgence such as food, sex, entertainment, wanting good clothes, etc... are akusala.

By teaching that sensuality is akusala the Buddha wasn't teaching that everyone must abstain from them or else they are being bad Buddhists, but rather that they don't lead towards Nirvana, and that renouncing them is superior, and that in the end when one becomes Enlightened, one will give up the desire for them. That doesn't mean that as practicing Buddhists we cannot enjoy sensual pleasures within moderation, but giving them up is in the long run a much better way of finding happiness.