An incredibly detailed World War 2 strategy game, "Hearts of Iron 3" will scare away all but the most dedicated wargamers.
Hearts of Iron 3 is a game where the player takes control of an entire country between 1939 and 1945. This includes military maneuvering (on a grand scale), production, supply, politics, espionage, and research. Naturally, this game is a bit complex - to put it lightly. To put it more bluntly, Hearts of Iron 3 is so dense and so complicated that even with the woefully understated tutorial there are still a billion things to keep track of at a time.
This is the primary thing about Hearts of Iron 3. Individually, its elements aren't that bad - if it was just a battle system, for example, it would be hard, but manageable, to figure out what's going on. The issue is that there's all the other things to keep track of as well. Every military unit has roughly 15 stats, and these are influenced by terrain, weather, and other conditions. To produce these military units, you need different resources, which requires holding different areas, maintaining proper policies, and so on. Each of these aspects is complicated in and of itself - the fact that you have to keep track of all of them makes it exponentially more complex.
Hearts of Iron 3 isn't a bad game per se, but it is a very inaccessible one. As mentioned, the tutorial only touches on basic concepts and then sort of leaves the player adrift to figure out what everything else is. In addition, the fact that it's World War 2 (and only WW2) means that it's hard to make a scenario where the player can easily "learn the ropes"; although one can always play as a smaller nation like Greece or Romania, this ends up being more difficult in the long run. If you play as a strong nation with a good headstart like Germany or the United Kingdom, then you have to manage a lot of territories from the get-go.
HoI3 at least has some sort of dynamic difficulty - you can delegate certain aspects of the game to the AI - but this is sort of a small compromise. It's still a very dense game, and the minimalist, basic graphics don't help. It's possible to download sprite packs, but they don't actually help that much. There's really so much going on that it's overwhelming no matter what. It's certainly complex and realistic, but it does these things in a way that makes it impossible to get into unless you are totally into that specific kind of gameplay.
Overall, it's not fair to call Hearts of Iron 3 "bad" or "unplayable", but it's pretty much implausible for the average person to play. There's just so much going on that it's overwhelming and the game doesn't do that much to try to introduce you to new concepts. If you're a dedicated strategy gamer looking for something intensely realistic, then give HoI3 a try. All others shouldn't even bother.