The X3 series is the "Master of Orion" or the "Elder Scrolls" of the galactic combat/trading genre.
X3 is complicated, and it may tax your brain's ability to keep track of everything. Science fiction isn't the fantasy genre. Commanding & configuring starships and participating in an interstellar economy isn't supposed to be dead simple. That's why I miss the complexity, and welcome its ability to challenge me again.
Do you want to control a sprawling merchant fleet?
Or own factories that create your own ships and weapons?
Or set up a complex supply chain of factories spanning many star systems?
Well you can in X3.
Want to own & fly carrier ships or a fleet of battleship class vessels? You can in X3.
X3 is the reigning classic of the open ended, single player, space combat/trading genre, because there are so many ways to fulfill that space opera itch.
There is however, room for more design improvements. For starters, the quest logs and player messages could be organized better, especially after it is filled with countless entries. In addition, the space between the jump gates is too crowded sometimes. This is especially evident when one is flying a gigantic capitol ship, or when one is trying to create a massive factory/industrial complex. If they could make space seem more "vast," by spacing the objects farther out, and compensate by increasing relative velocities, it would help a bit. Also, if there is a way to command wings of fighter craft easier, it would also be welcome.
Perhaps I'll find out if they made improvements in these areas in X3 Terran Conflict. I look forward to it (when I have time (shudder)), and these types games deserve to be made, far into the future...