ooh, astroneer is great! haven't played it myself but seen some gameplay of it. mine is Planetside 2 with about 2400 hours... most of that is from the past two years I'd say

Minecraft. I spent a lot of time on it, especially when playing with friends on my server.

Must be Civ IV - that whole series makes you lose track of time - start a game and that's the whole weekend gone; even now Civ IV with the Realism Invictus mod feels like it's got tonnes of gameplay still left in it for me.

That said, OpenTTD has been an enduring favourite of mine for the past few years and because of its flexibility it might surpass it in the long-term.

World of warcraft. Still true. I only played up through Crusade even. But it ate literally dozens of days of my life. I wouldn't say I regret that, as it was a learning experience for me. But I would definitely not have played wow if I could go back.

Parent here, very badly envious of all y'all's numbers.

(but in my pre-kid days I'm sure I put in at least 300 hours on the pre-Steam version of Dwarf Fortress)