Games have a positive and a negative experience at the same time.
During playing a game the primary chemical in your brain affected is dopamine. When we accomplish a task in a game it releases a hit of dopamine, this is the chemical that makes us feel good. The same chemical released when you finish a task in real life, eat food, have sex or engage in any activity you enjoy. Some drugs are addictive because they release this chemical.
Games like Candy Crush and others learned to “Hijack” the reward part of your brain. When you accomplish these small tasks of lining up crystals, it releases this dopamine in your brain. Making you happy and feel good. This makes you feel like you achieved something. The more you achieve, the more dopamine your brain gets. This can have an addictive effect and be quite fun.
However it’s not all bad as it sounds. Games also increase memory, learning, reflexes, hand eye coordination and even have a social effect if played online with friends. Some people prefer to interact this way. Stimulation of the brain in such a fast way helps the brain learn quickly and has even shown to reduce dementia and other aging brain diseases in older people. If grandma is playing games, she’ll feel younger for longer!
Game Designers can take advantage of this by whats known as the “addictive” quality. By using random chance chests in games that grant a reward. The harder you work for that chest, the more dopamine is released. Gambling also releases dopamine when a randomized system is added to game items.
However you don’t want the player working too hard, or the stress and frustration will offset the reward factor. It needs to be challenging enough to entice reward, but not enough to make someone push the problem away.
Overall the effect of video games can be addictive, but it is not dangerous or harmful in any way and can even be beneficial.