HoI is, by it's nature, a relatively complex game. However, if you're familiar with a bit of WW2, that's likely to help you get your head around things (as it's enough of a simulation, that generally doing what worked during the war will help ease your way into it) - I also found EU harder than HoI, just because I was less familiar with the history. HoI4's interface and structure is a huge step forward from HoI3 though, and I'd bet that if you're interested in a WW2 grand-strategy game, once you've got your head around it you're likely to enjoy it.
That said, I'd say the best thing to do would be to watch some of the recent WWWs, and a few vids after release, and see what you think of it there. If you can follow the streams after watching a few (and choose streams that'll talk you through things - most of the WWWs will probably be a little quick if you haven't been reading the DDs - best to wait until after launch and Arumba, Quill & Co have stuff out), you'll have an idea if it's for you or not

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