Maybe I will revisit 4 with some mods instead of buying this crap.
I've seen people recommend Realism Invictus, it got an update semi-recently and apparently it changes the base game a lot.
Can highly recommend.
Realism Invictus continues to be sporadically updated (about once a year), but other mods I can recommend would include
History Rewritten (essentially how I would imagine IV would have turned out if Firaxis just decided to keep developing it instead of making V, very tight gameplay but can be a bit unforgiving in how tight the balancing is),
Planetfall (a proper spiritual successor to Alpha Centauri),
RFC: Europe (probably the best RFC-based module, really wish that there more civlikes went down the RFC line of development - currently there's also an
enhanced edition that's in development),
Sengoku (basically taking the old Civ III scenario, porting it to IV's mechanics, then mixing in a bunch of ideas from Nobunaga's Ambition and TW: Shogun 2),
Sword of Islam (an aged RFC module inspired by the Broken Crescent TWM2 mod, but probably would be the best if Europe hadn't come around, currently there's also an
enhanced edition being developed). There's also other classics like
Pie's Ancient Europe,
Fall from Heaven II and its myriad
modmods (Kael, the developer,
is apparently working at Amplitude so there's a chance the upcoming Endless Legend II will be a spiritual successor to FFH) and
Caveman 2 Cosmos (honestly I can't bring myself to get into it, prehistory and space age speculation goes against the whole appeal of civilization for me).
Civ 4 is one of those games that you can pay $10 for, get an amazing base game of a few dozen hours, then spend a good decade enjoying free content that shows up a lot of professionally developed games.