Whether you started with a 2600 and a joystick in your hand, an N64 with a blistered palm or building your first PC in your teens, what is that one video game you've played at some point that to this day sits at the top of your list.
The music from Sim City (SNES) is on a perpetual loop in my brain and always will.
Edit: Also for your list - The Impressions Games 'City Builder' series (Caesar 1-3, Pharaoh + Cleopatra. Zeus + Poseidon, and Emperor: Rise of the Middle Kingdom).
My favs are Empire Earth (it was a shock having so many ages after playing AoE (2) and Knights and Merchants. This one was my first RTS and it is SO unique, I absolutely love it and have found nothing quite similar to it. There still is an active mod and multi-player community, albeit a small one
@pgetsos I recently got back into AoE2. It's still being updated (currently on version 101.102.whatever) with the help of community feedback. Also, there are more playable cultures and missions than I remember from my childhood.