Aside from relatively minor aspects like the attack options, the game levels don't tend to involve a wildly different experience -- yet they offer some challenges, including self-improvement. A current count of the number of zombies killed appears in the upper right corner of the screen in Survivor.io, and as their risk of perishing increases, the green bar that floats beneath players is gradually depleted. Kids can purchase upgrades to assist them in the game, such as enhanced strength, with coins they earned by playing or grabbed while walking around. When a round ends, kids will see the amount of time they lasted and receive coins and EXP. The game's backstory isn't too detailed -- kids basically just know zombies are roaming around a city, causing chaos. If there's an overall, far-reaching goal beyond moving from level to level, it isn't explicitly described.
Players are periodically asked to choose a skill to learn from options such as throwing two Molotov cocktails or a boomerang. The wording is a little misleading -- instead of getting instruction, they basically just receive an additional automated battle move. Logistically, the game can be a bit mixed. The controls offer fairly smooth movement, and kids can direct where their gun fires, but other weaponry is somewhat out of their control. Now, if kids are running low on energy to attempt the next level or try the same one again, they may need to buy more using green gems -- a currency that isn't thoroughly explained in the game. But although their gem supply can run low at times, it generally shouldn't diminish so quickly that they have to stop playing. Kids may find that the rounds feel repetitive after some time, even with some new attack skills to choose from. The app doesn't immediately prompt them to buy things to be able to play, though -- so if they're looking for a fairly simple game that will allow them to keep trying to beat their previous performance, Survivor.io may be a good fit.