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III - The best, well balanced, gorgeous art and music, can run smoothly on a potato and aged extremely well. And that's not even getting into the mod community's work. If you're going to play only one turn-based strategy game in your life for some reason, play this.
II - Excellent in its own right even if III had never been made, for a lot of the same reasons. Particular credit goes to some fabulous standalone scenarios that shipped with the game with clever challenges and good world-building - Colossal Caverns, Gates of Hell, Plains of Aekon and more.
V - Lots of fun as a game and has a ton of strategic depth even if the setting isn't all that original. The original campaign story is poorly written though the campaign gameplay is still good.
I - Everything Heroes I does, Heroes II does the same but noticeably better. It has some nostalgia value, especially if you want to try every Heroes game, but just get Heroes II.
Chronicles - Really compelling, interesting storytelling even if it doesn't fit all that well with some of the rest of the lore. I enjoyed playing this to the end and if you're into Heroes 3 you probably will too. Be aware that if you want any kind of *challenge* out of Chronicles you're going to have to set nearly every map to Impossible difficulty. Also be aware that there are thriving Heroes 3 mapmaking communities who have made lots of good stories with Heroes 3 that don't require you to spend any money or as much time.
VI - Fun to play, good balance, better writing than V and took some refreshing, novel approaches to core elements of Heroes gameplay. However, this game was held back by truly awful DRM and shipped with a lot of egregious bugs. The "Complete" edition you can find at this late hour lacks most of the bugs but not all.
King's Bounty - Still excellent for a thirty-year-old game. It has no replay value, but that's no reason not to play it once.
IV and VII - I will admit I haven't played these. Their reputation as games where enormous amounts of gameplay can be rendered meaningless by massive bugs is intimidating to this troper who doesn't actually have that much free time to burn. This is unfortunate as the writing was supposedly quite good for both of them.
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