1. Master of Orion 2: Battle at Antares
The best 4X game of all times is Master of Orion 2: Battle at Antares.
Hands down, no doubt, without question.
Even today, 20 year after its release, Master of Orion 2 plays like a masterpiece, nothing less. The immersive music, incredibly well designed races, balanced gameplay, mesmerizing turn based space battles, everything in this game has defined the meta rules of 4X games. Not only that there is a general consensus to this statement amongst the 4X player base, but the big majority agrees that MoO2 even trumps the best 4X titles of today.
There is not much more to say about this game, except that you should go and play it even if you are not a huge fan of the 4X games. It has depth, charm and a quality that most games from today are missing. In my own personal recommendation, it doesn’t only belong at the very top of 4X strategy games I have ever played, but is also one of my favorite games of all times.
You should grab the Master of Orion 1 & 2 bundle on GoG.com.