I used to play this with 4 or 5 people in college (80's) and enjoyed it. Recently I've been listening to the Rex Factor podcast, and I have a hankering to play Kingmaker again.
I have brought the game down off the shelf for the first time in at least 20 years, and I'm on the verge of trying to remember how to play. Problem is: the only other player I can count on anymore is my wife...
So, how well does it play with 2 players?
Also, in your opinion are there more modern games that have "replaced" it for you?
I think it would be perfectly playable. I'm not sure that it would be particularly interesting.
IMO a lot of the fun with the game is the jostling of the various factions, the whittling-down effect, the occasional rising up of a faction once considered puny suddenly returned to strength, etc. You're not going to see a lot of that in a 2-player game.