4) The Great War (WW1)
One hundred years ago, Europe was embroiled in a conflict that shaped the future of modern Europe. Now, you can are put in a position where the stakes are high, with any move potentially resulting in a major conflict. Alongside a major focus on the European theatre, the mod places attention on revolution in Mexico and China, as well as Italian desires for African expansion.
Furthermore, the Great War mod includes focus trees for major powers, alongside unique units and two scenarios (one starting 1910 and the other in 1914). The mod brings events like the The Assassination of Archduke Franz Ferdinand and The October Revolution to enhance the real-time historical experience. Additionally, there is plans for more content in the future, all of which can be found on the mod's Steam Workshop page.
3) The Road To 56
This mod looks to balance the overall gameplay of the game by offering more unique national focus trees to nations such as Brazil, Tibet and the United Kingdom allowing you to explore different historical paths. There are no prizes for guessing that the game runs until 1956 as opposed the shorter time the vanilla mod runs until. With this, the mod includes more units, a developed troop experience system, laws and new releasable nations.
In essence, the Road to 56 mod basically enhances what you get in the standard vanilla mode. Moreover, the mod receives plenty of updates and bug fixes and has obtained positive reviews from fellow gamers, despite some important nations missing unique focus trees. From my own personal experience, the mod is enjoyable to play. So, if you're interested in reading further details – see the mod's official page.
2) Millennial Dawn
The 'Modern Day Mod' is the highest subscribed mod for Hearts of Iron IV, which immediately highlights the high popularity of this mod. Furthermore, the mod won the "Outstanding Modding Achievement" at this year's PDXCon 2018. MD offers two scenarios, with one starting in 2000 and the other 2016.
Personally, I think the mod is great due to the fantastic use of the decision system, that came as part of the Waking the Tiger DLC allowing for a greater consideration of alternative history options. With that, I particularly enjoyed revoking Article 8 as Japan, reforming the Soviet Union and becoming communist Britain. To see what all the fuss is about, you can read the details and feedback on the MD official page.
This mod takes place in a world where the German Empire succeeded over the Entente forces in the First World War. Therefore, this sees Germany as the dominant power in the world, with Britain and France retreating to policies of isolationism and turning to the ideals of Karl Marx.
Kaiserreich boasts a stunning political system that builds upon the foundations of the vanilla mode alongside unique focus trees for most nations, with additional plans for every nation to have one soon. Although more people subscribe to the MD mod, Kaiserreich is the second most subscribed and is mainly popular due to the exploration of different alternative history paths. To read the full details, check out the mod's page. If you decide to the play the mod, I would recommend playing as the German Empire or the Ottoman Empire.