Mine is playing AOE2 in easiest (or standard if I want a bit of challenge) mode against 3 bots. I just build my economy, wall up (and laugh at the enemy soldiers attacking my walls in vain), reach imperial age and attack once my army reaches the population limit. I also send 104 in the chat so they don’t surrender and I can enjoy razing their all buildings one by one. If any of them builds a castle, even more fun. A build a trebuchet and watch it raze the castle from a safe distance. If there is sea, after I am done with the land, I build 3 docks, do research and build a navy and hunt down ships around the unxplored sea. It is fun, satisfying and relaxing.
What is yours?
I found this post while playing AoE2. I enjoy playing the campaign a lot because there are so many and because of the sandbox gameplay.
So I can pretty much infinitely play them and have done so from time to time since it launched :)