I'm writing this three years after launch.
Don't be fooled by the frequent discounts, there's a reason this game is *always* on sale:
STRONGHOLD 3 IS CRAP.
Even if they were giving it away, it would still not be worth the download. It's a messy, buggy resource hog.
In my first experience, the game would freeze for 10 seconds every minute or so. I endured that BS for ten minutes and then it crashed.
Most of the three hours I got out of this game were spent in the map editor. None of the maps I made could be played.
I've made a large map exactly the same way I used to do in SH2. It failed to load.
I've reduced the large map to a single castle with a few trees around it. No enemies, no animals, not even a river. It failed to load as well.
I was able to load a medium custom map but the game would keep freezing over and over, making it unplayable.
I couldn't even play the campaign. As the "game" was only taking space in my HDD, I uninstalled it.
Even if you're into games that crash often and slow down to a crawl for no apparent reason when you're running it on a machine that's WAY above the recommended specs, there's a lot of better options out there.
Even if you're a die-hard Stronghold fan like I used to be, and if by some miracle you can get it to run, you will find out that Stronghold 3 brings less of the same, as they removed several cool features that were present in SH2.
Support is nonexistent as developers did not deem it commercialy viable to keep patching this failure of a game and have decided long ago to focus on their next rip-off instead, so it's pretty much abandoned now. All the patches this game will ever receive have already been released and they weren't nearly enough to solve the major issues that still plague this title.
FireFly will have a hard time convincing me to buy anything from them in the future. My advice?
Go waste your money somewhere else. This is not the entertainment you're looking for.