Pulled from my Top Playtime on Steam (so you know you'll get your money's worth if you like them!)

• Factorio (Even though the DLC is pricey, it at least doubles the playtime. Though, like RW below, it takes a lot of content/concepts from fan-made mods.)
• RimWorld (Though I dislike how many DLCs they're pumping out and how much is basically taken from mods.)
• Terraria
• Mount & Blade (Warband 1 & 2 are prime)
• Kerbal Space Program (NOT the sequel)
• TerraTech (The original is a better experience)
• Both the Pathfinder games
• Grim Dawn
• The Riftbreaker
• UnderRail
• Mindustry (Open source/free, but deserves the support from buying it on Steam.)
• No Man's Sky (They've gone above and beyond in shaping up since the clusterf release.)
• The Long Dark
• Rise to Ruins
• Space Pirates and Zombies (1 and 2 are both great, in their own ways.)
• Caves of Qud
• Tales of Maj'Eyal
• STALKER (I've heard bad things about #2, but the rest are great, high replayability with Anomaly.)
• Astroneer
• War for the Overworld
• Autonauts (and Autonauts vs Piratebots!)