X3: Terran Conflict. A hidden gem. The game is huge - even 100 hours in, you'll still be learning new game systems! The random missions get terribly repetitive but there's so much to explore and exploit that it won't matter. The story missions are... different. Instead of telling you to go from point A to point B to defeat the dreaded Ks, they set much bigger goals and let you figure out just how they will get done. Sadly, the DDTC mod is no longer around but there are plenty of others to have fun with. I wouldn't bother with earlier games at this point. X: Rebirth isn't nearly as bad as some say with a few mods thrown in but you won't have time for it - move on to X4 after X3.
BattleTech. I don't think I modded the game at all but, if there's one to make the UAC weapons rarer, grab it - those things are entirely too good. After this you'll probably be wanting to play the new XCOM. Maybe. Troubleshooter: Abandoned Children isn't as well known but it is actually better. Thing is, it lets you pick from a crazy number of skills. When I played it, I had seen nearly all those skills in one form or another over decades of gaming. So it might be best to keep it simple with the new XCOM games. Then look at T:AS.
The Witcher Series. Witcher 1 is pretty fun but pretty old. There's a nasty difficulty spike (you can guess what that means) fighting a spectral dog but, once you're past that, the game really is fun. Witcher 2 looks far better but wasn't as fun for some reason. Witcher 3 was incredible! Handle the first two games however you will - just make sure you get to that third game! Tell Trish I said... oh, actually, maybe you shouldn't mention me. She might still be mad.
Final Fantasy 7. Timing will be tricky here. The original game is VERY old. Mods can help it a lot but there's only so much that can be done. The story is really well done, though, and it has great game play and music. The timing is tricky because they are releasing a re-make. They're expanding the game into some unknown number of episodes with graphics that are soooo much better! One, the other, both... I don't know.
Outer Wilds. Quick, fun, and lighthearted. Try not to even see any screenshots of it - just get it, install it, and play it. Might want to have a bag of marshmallows handy.
Subnautica - another one I won't tell you a thing about, other than it is a good bit longer than Outer Wilds and has some base building.
4X Games: Jeez... most of the entire turn based portion of this genre. Probably start with Endless Space 2 because it's not only fun but really easy to get into. Civilization 5 is that way, too. (I couldn't get into Civ 6.) After those, Sword of the Stars, Galactic Civ 3, and Endless Legends are fun, too, but I don't know if there will be time for them before some new 4X game shows up.
Saints Row 3: just plain old fun. Yakuza 0 is also crazy fun, but has a serious story running through it as well.
There's so many awesome games of the past (many from BioWare) that were so much fun at the time. If you were to retire and the game industry would stop making new games, you could probably get through the highlights in under ten years but that's not going to happen.