One suggestion for Strategy games that has been overlooked here is
Sword of the Stars - Ultimate Edition + Argos Naval Yard
http://www.impulsedriven.com/sotsult
The game is totally awesome, basically it plays like a Total War game but in space. That is, it has a turn based strategic mode, and a RTS battle mode. Except, IMO its better than Total War.. which i saying a lot because I like Total War games as well.
It has tons and tons of different tech, and your tech tree changes from game to game so not only does it seem like there is always new stuff to discover, but you are always having to evaluate how to make the best fleets and defenses from what you have.
Ship building is detailed, and working your tech tree to construct the coolest fleets is just awesome. The stretegic mode has the perfect balance of macro/micro, you have some meaningfull control over your planets but it does not take a year to manage your empire each turn.
The game has basically been expanded and perfected over the course of several years and 3 expansions, and is now what I would consider an "unknown classic"... and it even has a full fledged strategic multiplayer.
A must have game for sci-fi fans who like Total War type games.
