I need to check out some of the games mentioned here but as of now, feeling rather delighted to be back to Heroes of Might & Magic V (both expansions) after Age of Wonders 3 just doesn't feel finished and sub-par (although their way of tactical combat system is a bit superior to HOMMV but the magic sucks big time -.-)

I have to go with Sid Meier's Civilization II, but part of that may be that I can no longer play it (it won't run in Win8-8.1).

Honorable mention in my case goes to MOO2 and Civ V BNW.

no love for Warlock out there?  I got a lot of hours in that game.

I played a lot of it too, good fun without a doubt but just a few too many flaws to be one of the greats. Plus might not be hardcore enough for many but yeah, good times. Never got the 2nd one though as it looked so similar to the first and I really wanted simultaneous multi-player like in Civ 4 but it still doesn't have it sadly.

Warlock/Warlock 2 is sort of a disaster on many fronts.  It's AI is laughable, it's almost entirely PvE even at the hardest levels because the environment is the only real challenge to surmount.  The races are in no way even marginally balanced, nor are the spells.  Most of the challenge is also random, and as such is unreliable.

It's a wonderful player side design, streamlined and intelligent 4x features with good diversity, but it's entertainment only because 90% of the difficulty is random spawns that may or may not be a problem for a particular player.  I rate it fairly low as a strategy game, even if I do have fun with the idiocy that it is.

Sword of the Stars 1 with all the expansions.

Moo2, Alpha Centauri, Galciv2, HoMM2, Civ2/4, Stars!, Final Fantasy Tactics, X-COM, XCOM.