A nice selection of songs for Cities Skylines I often listen to while playing.

Makes dealing with monarchies much easier. The Great Powers mechanic is interesting enough to justify this DLC.

Brings EU IV to a whole new level.
Overhaul of war mechanics is much better than base game.

Getting this for EU IV is just common sense...

This smaller DLC for Crusader Kings 2 adds a lot to the roleplaying of the game. A lot of new possibilities to expand your characters. Focuses help to improve the skills of your chosen ruler and the new events make the game much more immersive for me.
Definitely one of my favorite expansions.

Communist France ally with the Soviet Union against the capitalist enemies of United Kingdom and United States after they defeated the German Reich and split up central Europe among themselves?

All possible with some patience and the right decisions...

Another nice grand strategy game by Paradox, not that great as EU IV or CK II, but I love it just the same. Never played HOI III so I cannot say something about changes.

I like how you can set up different divisions according to your tech level and the idea of setting up battle plans and carry them out afterwards.

But the strongest point in my opinion is the possibility to play around with history.