Fuggen love mods, with XCOM 2 for example I put in a tank one for Advent and XCOM that I forgot about it but then encountered one in the skyscraper in the 2nd last mission and I only had a mech and 2 supports. It's supposed to be a stealth mission but the tank drove over all the cover destroying it and constantly peppered the area with explosive shells. Needless to say that fight was tougher than a Chosen fight.
Let me list off some games:
Darkest Dungeon is another great one but I'd recommend no more than 20 custom classes, the game chugs and will bug out under all that weight. I love
the Thorn class. Defensive marker in default but becomes Riposte-Dodge-Bleed stacker in attack mode.
Guts Is also another good one if a bit on the cheating side. He singly handily got me to 300+ kills in the Color of Madness gauntlet. Never finished though, game bugged out at week 70.
Mass Effect has good mods. There are modding guides
for all 3 games if you want to get into it.
Nier Automata has good graphic mods, Yakuza has mods that restore licensed music, Persona 4 has mods that add in stuff from the Vita port, high quality audio for example. Wish Denuvo was gone though, it'd make modding so much easier. Custom campaigns for Shadowrun,
Caldecott is about a train robbery, it's great. There's also the
original Dead Man's Switch campaign in Hong Kong, meaning new weapons and cyber augments. Stardew Valley has entire expansions that I'm not touching yet for more content to be developed.
Ah, Kotor has Deadlystream and you can find mod builds on r/kotor. Witcher 3 had a simple one of leveling legendary weapons alongside Witcher gear, meaning that they'd be actually useful and look cool.
This is just scratching the surface for me, stuff like Dragon age Origins, FNV and ME3 are so much fun modded I don't want to go back to the vanilla.
The next major target I wanna mod is Total War Warhammer 2 but I don't have the $200 to get all the DLC and such, so need to wait for a proper pirate copy, then figure out how to get the mods working off the workshop. Modding Stellaris so that mods worked in the GoG version was kinda the same way, maybe buy base game, download mods, copy to GoG files, rewrite scripting in a file. Bam, should work.
Speaking of Stellaris, you have stuff like the Gigastructures, planetary diversity (Able to colonize molten worlds for Forge Planets is a godsend for alloy production) but the one I found the most fun was
Unique Ascension Perks. Cortana for example acts as a 4th researcher selecting a random tech every 5 years to research, even rare or unique ones you can't get normally. L4D2 has
Fat Bastard for a Boomer and give him a Stay-puff skin and he's this really agressive marshmellow man that screams "I've got bigger titties than you!"
I love modding.