well if you want to paid 20$ for 5 mission that you will repeated till the end good for you but there are F2P game out there that actully, have a good story line a load of play time and that the dev team are always adding into the game. All of wich is free here some exemple: Dota LOL Warframe Path of exile Planetside 2 Rift Firefall Loadout star conflic ect