According to Steam the top 3 are:
But that of course does not include the games not running from Steam and pre-Steam games. So World of Warcraft is somewhere in there too. And the final Top 1 must be Transport Tycoon Deluxe (even if you don’t include OpenTTD).
That would be a horrible experience: You sign up (even if it’s just for a dollar) and then you would have to wait a month until you can play the new stuff. This way they are still giving away the single player campaign and one month of multiplayer for a fraction of the original price. If you want to buy the game it might even be cheaper to sign up and buy it with the included discount and then cancel again.
What I meant was that it will not be that hard to replicate. It might feel complicated and deep but most likely isn’t that complex. Sure - without analyzing the original source code (which isn’t legally available as far as I know) - it might be impossible to recreate the exact behavior, but it should be possible to mimic the behavior - it might just take a few attempts to fine tune the input parameters.
I started playing it last year because my nephew wanted someone to play (apart from his friends at school). I kept playing it on a regular basis (I had bought the base game years ago, but have not paid anything since). I enjoy the colorful graphics which run fine even on my 10+ old gaming PC. Some rounds are short and you’re dead within minutes but often I reach top ten, but even then the rounds aren’t taking that long (20 to 30 minutes), which is something I like about the game, because I barely take the time to have hour-long gaming sessions any more. Despite its looks skill makes a difference when it comes to aiming and movement (most special weapons are movement skills). I mostly play the no building mode because I can’t manage shooting and building at the same time.
I’m pretty sure you could train an AI to play a game like Civ, but the problem stays the same. As everything progresses to get more complicated and you have to decide even more every turn it gets harder and harder to train. The results are kind of unpredictable and you might have to train your AI again with every patch. It will limit the systems your game can run on (even excluding some platforms) and heavily impact performance on the systems it can run on.
The gameplay stretching out in later rounds is also what makes the AI so hard to improve. There is just too much to do and the effects are too complex to understand for a classic game AI. If they simplify the gameplay with the player progression into later ages it will also make the development of a competent AI more likely.
But to be honest: I doubt anything like that is going to happen. Even when controlling a planet wide empire I will have to decide what every city is going to do next and what every unit is going to do in the next turn…
The final boss fight was good though. It fits the character and the final cutscene hit the tone of the series in my opinion.