HOI3 is probably the most "micromanagement intensive" game in the series, but you can automate a lot of functions (with various quality results) to relieve some of the tedium. If you don't mind digging in and manually assigning leaders to 200 divisions to get the most out of them (the AI has the distressing habit of putting your best armor leaders into port garrison units, your best urban defenders into recon units, etc.), and don't mind occasionally moving Corps HQs to stay within radio range of their subordinate divisions, then this game is for you. If you want something that's more "grand overview", then you probably want to stick with HOI2 and its mods and spinoffs.
HOI3 was originally intended to operate from "realistic" historical starting conditions and "evolve" into whatever political situation developed from there, but a few fundamental AI flaws made it almost unplayable. The quick and dirty fix was to rip out all of the complex diplomatic mechanics behind the scenes and replace them with simple scripted actions, putting the game "on rails". The rails were improved, and branches were added, but it's still got some funky baggage where things are forced into a historical "outcome" even when the situation in-game is totally different. For example the US will end up with a piece of Germany after the Axis falls, even if the US was never involved in the war. Germany occasionally sends FAR too many troops to Norway, resulting in manpower shortages on the Eastern Front while 50 divisions starve in the mountains of Scandinavia. Wargoals allow you to claim regions A or C, but not B for some unfathomable reason. It's a long list, but most of them you can eventually figure out how to avoid or work around.
It's strictly a matter of personal opinion whether or not the game is worth the steep learning curve and occasional nonsensical situation. I'm still playing it, despite the flaws, because there's no better alternative out there; overall, a "good" game that could have been incredible except for a few really annoying problems. If you detest micromanagement, then you'll hate it.
