There are two singleplayer games that immediately jump out in my mind as titles I would recommend with absolutely zero hesitation.
RimWorld is a phenomenal sim game with huge storytelling value, absurd gameplay possibilities, and the best modding community I’ve seen in a game outright with respect to both quality and quantity (I run over 200 well-made mods with negligible performance impacts, it basically puts Skyrim to shame). The price is a bit on the higher side, but it is the only game in my entire Steam Library that I paid full price for without any regrets. The relatively new Royalty DLC is in no way required to get the most out of the game; though it does add some neat things, it’s more to support the devs honestly.
Brigador: Up Armored Edition is a truly hidden gem. An isometric sci-fi mech/vehicular combat game, it was an commercial flop on release in 2017 (due to being unable to generate enough publicity) despite having a unique and well-executed mix of mechanical depth, deep worldbuilding, excellent dystopian synth soundtrack, gorgeous artstyle, and satisfying gameplay arc. (Brigador is actually on sale right now at a historical low so I’d genuinely recommend snagging this one)
RimWorld is a game you can lose hundreds of hours to with ease in sustained sessions, while Brigador is great in quick stints of intense tactical action. They complement each other well in my library and they will in yours as well :)))
