This game is highly addictive for a puzzle game. even though you can buy stuff in-game, you never need to if you play for a bit everyday. Note: Steam and mobile versions not linked.

An awesome first person Zombiepocalypse game where you can legit jump, climb and parkour off of most everything. Tons of content, and challenging gameplay ( you can't shoot your way out of everything)

AoE is the definitive RTS in my mind. Years and years later it has new expansions and still has a history-laden plot; man it's so good and addictive. Online battles are a blast. NEVER GETS OLD.

Vran is an ARPG with an awesome transmutation system to upgrade your weapons and spells and clothing. It has a linear storyline with many sidequests and bonus content. Co-op is beyond awesome.

Terraria, boiled down is 2D Minecraft. But it's so much more. With limitless possibilities in terms of building fun things and editing your generated world, it also has tons of mods to add even more.