Once you get past the learning curve, you'll have fun with the game, lots of it because the game is a naturally addictive and fun game and it has tons of replayability. Although, it is plagued by nonsensical problems that as a new player you'll be confounded as to why they don't exist. When you get in a massive stalemate(New player as Russia against Germany) and realize there's no way to make peace. Completely boring sitting for 4 years in a war with no borders changing and then just quitting the game(if you do turn the war around, it is quite fulfilling), or as Germany, you have to capitulate America to win the war, and there's no way to make peace with them through diplomacy if you become unable to reach their lands; even after defeating Britain and Russia.

Naval invasions require large pre-emptive planning; invasions, which can take a hundred days to prepare, 20 minutes IRL depending on how much divisions the ai has spammed; you saw no use when paradrops(which are scary in this game, very scary sometimes) did the job against Britain and Norway. Don't hope to meet sizeable resistance unless you have a large force of marines as the battle for a beach foothead could take another 50 days and at that point, you'll likely lose it as they'll move a few more divisions into the battle.

Shore bombardment is the way to go if you have naval supremacy. And sadly, even without much of a navy, it is extremely easy to beat all of the allied navy as Germany when you get the hang of it; submarines are effective in combat if you have a ton of them(and a ton of them is easy to get; they are extremely cheap). Naval bombers will completely annihilate Britain's navy in the English channel, and they won't even bother moving their navy there which easily let's you invade the mainland

At the start of the game, you can justify a wargoal on France and capitulate them without a fight in a year with a few paradrops due to their national spirits. No world war started for France; Britain can't back them up in my before they're dead.

The game is a joke once you have a grasp on the game mechanics because the AI does not.

One of the goods thing about HOI4 is the mods, Old World Blues(a mod based on Fallout) is awesome, and so is Kaiserreich(What if Germany won WW1?), there are tons of great mods, although most large ones are plagued by the game's design choices; especially the AI. The game is like an early access game, and buggy as hell.

If you do play the base game, play only the recommended nations or you will run into a lot of stupid design choices. I personally recommend Germany as the game is effectively built for them so they have the best pacing, and even with all it's problems it is still probably the most fun, then Japan, then Britain. Soviet Russia is good to learn the game, but be sure to build a ton of outposts(lvl 5 and above will do the trick) along your European border as if you are new, you want to be sure you don't lose against Germany.

If you want to learn naval combat, play America and wait for Japan to do something stupid, but be sure to combine your pacific battlefleet, maybe split off a few destroyers for patrols as the way it is set up at the start of the game will only get your navy annihilated piecemeal by Japan.

The game itself doesn't hold up to standard, with terrible AI for everything that is controlled by the AI, and dubious design choices. It's not as complex as most paradox games, so it's better for you if you're just getting into grand strategy but it is by few means a good games.
I recommend if you are new to Paradox/ grand strategy games, love World War 2(Th-the trials and the tribulations of the Allies, not the Nazis or anything!), or want a fallout grand strategy experience; Old World Blues is very good.
If you don't particularly enjoy WW2 experiences, I recommend Stellaris, there's a lot more effort put into that game and the inspiration can be seen.

Once you get past the learning curve, you'll have fun with the game, lots of it because the game is a naturally addictive and fun game and it has tons of replayability. Although, it is plagued by nonsensical problems that as a new player you'll be confounded as to why they don't exist. When you get in a massive stalemate(New player as Russia against Germany) and realize there's no way to make peace. Completely boring sitting for 4 years in a war with no borders changing and then just quitting the game(if you do turn the war around, it is quite fulfilling), or as Germany, you have to capitulate America to win the war, and there's no way to make peace with them through diplomacy if you become unable to reach their lands; even after defeating Britain and Russia. Naval invasions require large pre-emptive planning; invasions, which can take a hundred days to prepare, 20 minutes IRL depending on how much divisions the ai has spammed; you saw no use when paradrops(which are scary in this game, very scary sometimes) did the job against Britain and Norway. Don't hope to meet sizeable resistance unless you have a large force of marines as the battle for a beach foothead could take another 50 days and at that point, you'll likely lose it as they'll move a few more divisions into the battle. Shore bombardment is the way to go if you have naval supremacy. And sadly, even without much of a navy, it is extremely easy to beat all of the allied navy as Germany when you get the hang of it; submarines are effective in combat if you have a ton of them(and a ton of them is easy to get; they are extremely cheap). Naval bombers will completely annihilate Britain's navy in the English channel, and they won't even bother moving their navy there which easily let's you invade the mainland At the start of the game, you can justify a wargoal on France and capitulate them without a fight in a year with a few paradrops due to their national spirits. No world war started for France; Britain can't back them up in my before they're dead. The game is a joke once you have a grasp on the game mechanics because the AI does not. One of the goods thing about HOI4 is the mods, Old World Blues(a mod based on Fallout) is awesome, and so is Kaiserreich(What if Germany won WW1?), there are tons of great mods, although most large ones are plagued by the game's design choices; especially the AI. The game is like an early access game, and buggy as hell. If you do play the base game, play only the recommended nations or you will run into a lot of stupid design choices. I personally recommend Germany as the game is effectively built for them so they have the best pacing, and even with all it's problems it is still probably the most fun, then Japan, then Britain. Soviet Russia is good to learn the game, but be sure to build a ton of outposts(lvl 5 and above will do the trick) along your European border as if you are new, you want to be sure you don't lose against Germany. If you want to learn naval combat, play America and wait for Japan to do something stupid, but be sure to combine your pacific battlefleet, maybe split off a few destroyers for patrols as the way it is set up at the start of the game will only get your navy annihilated piecemeal by Japan. The game itself doesn't hold up to standard, with terrible AI for everything that is controlled by the AI, and dubious design choices. It's not as complex as most paradox games, so it's better for you if you're just getting into grand strategy but it is by few means a good games. I recommend if you are new to Paradox/ grand strategy games, love World War 2(Th-the trials and the tribulations of the Allies, not the Nazis or anything!), or want a fallout grand strategy experience; Old World Blues is very good. If you don't particularly enjoy WW2 experiences, I recommend Stellaris, there's a lot more effort put into that game and the inspiration can be seen.