X3: Terran Conflict is probably one of my most played X games other than X2: The Threat (had it on CD prior to it's steam release). It aged really well in my opinion, brought new levels of scale to the universe, the story (though can easily be dismissed) was decent, the ship designs where fresh but kept somewhat of the aesthetics from the prior instalment and it has a lot of improved mechanics as well and ease of use.

As an entry point, might be better to go to Albion Prelude as it builds upon the universe and technology with a few more mechanics but this will always be my go-to X-Game.