I’ve enjoyed many Sid Meier games: Gunship, F-15 Strike Eagle, F-19 Stealth Fighter, Sid Meier’s Pirates!, Civilization (many versions), Colonization, Alpha Centauri.
..and Will Wright games: SimCity (many versions), The Sims (many versions), Spore.
Also: Kerbal Space Program, Populous, Second Life, Warcraft, World of Warcraft, Age of Empire.
I’ve played X-COM, it was very addicting but I hope to not pay it again.