3. Endless Space
Endless Space was a wildcard nobody expected, but the french gaming crew that goes by the name Amplitude Studio has managed to create an awesome, fetching 4X universe, by investing into their fans and listening close to their demands. Very quickly this game rose to the top, creating a huge fan base and propelling their game to the top lists of the 4X genre. Several well accepted expansions followed, perfecting and deepening the gameplay. Today, without a shred of doubt, we can say that Endless Space belongs to the top titles of 4X space games.
Now, there is currently Endless Space 2 in early access, which is promising to be been better than the existing game, but I will be patient and wait to learn more before I proclaim the successor as belonging among the top ten 4X games. We will probably know the final answer within some six months (which would be my own personal judgement).
In the mean time, I would suggest you to get Endless Space on Steam, considering that there are going to be a lot of special offers for that game as the sequel is being pushed forward (matter a fact, there is a 75% off deal as I write this, but will probably have expired by the time you come around to read this article!).