The short-session angle is what keeps Minecraft in rotation for me too, though I usually end up doing more than I planned. On HEAT, the grind question is the one that matters most to me as well; a free-to-play loop only holds up if the moment-to-moment play is fun before any progression kicks in. Your point about Deron and Nin Online rewarding persistence fits how those older-style online games tend to work, they ask for a routine rather than a quick visit.