It's a shame someone hasn't updated Command & Conquer Generals: Zero Hour so that it can be played on Windows 8.1. It's a classic game, and deserves to be mentioned in this list IMO. I used to love playing the GLA and steamrolling over the Americans *evil laugh*! ("Thank you for the new shoes!" :-D )
Another game that I bought only four days ago is Rise Of Nations, and I'm really enjoying it. It's great fun to start a game with spearmen and slingshot warriors, and end up planning missions using fighter and bomber aircraft. And of course if you want to go really crazy, you can develop nukes too. Great scope for varied strategy and tactics.
Apart from those omissions I think this list is very interesting. I own 10 of the 20 games mentioned, so there are a few that I'll be checking out and possibly buying, especially if they're in a Steam sale. Thanks for updating the list!
Don't know how about you, but I have C&C Generals: Zero Hour on Origin and it works fine on Win 8.1.