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I'm mainly asking about the games that were designed to run in Windows. Most of the reviews are about how the games need additional community patches and fixes to run. I so wish I could just download and play the games. I'm mainly interested in MM5 through MM9.
I've been trying to tun M&M VII for years, tried again tonight, and it hangs my Windows 10 system.
They were designed to run in Windows, at least from VI onwards. But Win 10 was still not invented back then, so it's hardly fair to call the whole series broken.
So yes, if you experience problems, you probably need a third party patch. Another thing that was not invented back then was widescreen monitors, so something that keeps that aspect ratio (instead of an ugly, stretched image) on modern monitors is also nice.
The series works just fine on win 10 as long as you install some extremely easy-to-find patches.

If you can't run it, it's your system that doesn't work.

Also, disconnect any and all headset cables from your PC if MM9 refuses to start. MM9 does not like some headsets for some reason.
MM5 is part of MM4/MM5, which are DOS games. They run in DOSBox, and should be fine.