THIS GAME IS AMAZING. this is the most comprehensive, most complete game I've seen in any gernre. It's definitely the type of game you need to invest time into learning. There is a deep learning curve but once you get a feel for the game, it makes sense why its so difficult to learn, because it basically lets you control almost anything. The game dynamics are amazing and very complicated but then again, so is global warfare. There is a great community of devoted HOI3 players who have answered literally every question related to this game so if you get it and find yourself not understanding the game dynamics, such as the supply situation, you can easily go online and read up on it. The supply dynamics, while sometimes buggy, is one of my favorite aspects of the game. If you're invading Western france, make sure to get large ports and not to outpace your supplies, less you fall victim to an axis counter attack that finds your front undersupplied and pushes them back in chaos. I like how the game manages the organization of the troops, both in terms of command structure and in terms of the org of the specifc unit. If they're under supplied or disorganized, they'll fail in an attack and soon you'll find the enemy routing you across the continent. It really takes a great deal of practice and patience to mount the correct offensive. You get a sense for how underprepared offensives can go awry in a second, especially when playing as Germany and trying to raise through the Soviet Union. You might get within 2 provinces of Moscow before you realize that you're supply lines havent caught up (because you didnt research the techs you needed) and then the Soviets counter attack with inferior forces and you have to scramble to recover. Thats the fun of the game though. You can prepare all you want but if things dont work out the way you planned, you often have to plan on the fly.
I played as the Soviet Union and thought I was perfectly set up to protect the mother land against the germans but got my but handed to me three ways to leningrad. It was the game of my life, reorganizing and launching desperate and doomed counter attacks to slow down the germans while I get more troops ready. It's very interesting because when you play as the Soviets you get the impression that the germans better conquer you within a year, because if they dont, you can create about 10 infantry divisions a month and thats a pace the Germans can't ever sustain.
Anyways, this game is amazing. You can play as anyone, Brazil for example, and work just to contribute a tiny amount to the war effort. Or you can play as the US and let Europe be while you focus on hunting and eliminating Japanese carrier groups that you know they can't replace the way the US can. Nimitz, Halsey and Spruance to the rescue!
If you like strategy and grand warfare, give this game a try, If you take the time to learn it and you understand what kind of game you are buying, you will not be disappointed!