Yes, X4 is a game that requires a lot of time and research. When I was playing it a lot I was watching YouTube tutorials, scouring the Steam, Reddit, and EgoSoft X4 forums, and Googling a lot. I really like space sim games and 4X strategy games, X4 is a great blend of both, there is no other game like it. It’s not perfect, I would like better AI and a better/bigger map, I always say Elite Dangerous is a mile wide and an inch deep but X4 is an mile deep and an inch wide.
I’ve played L4D2 (Left for Dead 2) for hundreds and hundreds of hours over quite a number of years. Love the game. I’m also now playing “B4B” (Back for Blood), but they’re trying to iron out a number of issues with it. I don’t think there’s a third.
I tried X, X2, and X3 (forget which one), but they never quite grabbed me for some reason. I believe I played X more than X2 or X3.
The later games catered a bit more to actual flying. My goal was complete economic dominance of the universe, which by the end consisted of staring mostly at spreadsheet-like lists of ships and factories 
. If you actually like piloting your ships, X4 is probably the best of the bunch. I never played the original X.
Counter-Strike
3,558 hrs
Last played: Oct 13, 2016
Counter-Strike: Global Offensive
1,382 hrs
Last played: Sep 2, 2020
Max Payne 3
704 hrs
Last played: Apr 23, 2017
I started playing the original Counter-Strike before Steam even existed, so the actual hours for that game I could only guess at, but might even be twice the amount shown or more.