Endlessly replayable with some good atmosphere and crunchy sound design. Whatever you'll do, there's always button sounds to send home you are doing something and progressing in your goals. Added to focuses and researching technology, and you have pretty good stimulation even around the main gameplay.
While I definitely recommend starting without DLC's enabled and enabling them one by one as you become comfortable with the mechanics you have, you could theoretically work around this watching some tutorials on YouTube.
Here's a problem with the learning curve in HOI4 though: It's certain you will watch a tutorial for something at some point, especially template designs or machinery designs, but in my experience: Don't be like me and do pay attention to recent template designs tutorials by YouTubers. They can do some crazy stuff. It will save you hours of frustration.
In spite of difficulties at improving in areas, or multiplayer being basically impossible, there's a reason we're 8 years into the game's lifespan and it's still beloved. Lots of DLC required though.

[b]Endlessly[/b] replayable with some good atmosphere and crunchy sound design. Whatever you'll do, there's always button sounds to send home you are doing something and progressing in your goals. Added to focuses and researching technology, and you have pretty good stimulation even around the main gameplay. While I definitely recommend starting without DLC's enabled and enabling them one by one as you become comfortable with the mechanics you have, you could theoretically work around this watching some tutorials on YouTube. Here's a problem with the learning curve in HOI4 though: It's certain you will watch a tutorial for something at some point, especially template designs or machinery designs, but in my experience: Don't be like me and do pay attention to recent template designs tutorials by YouTubers. They can do some crazy stuff. It will save you hours of frustration. In spite of difficulties at improving in areas, or multiplayer being basically impossible, there's a reason we're 8 years into the game's lifespan and it's still beloved. Lots of DLC required though.