I just bought and downloaded M&M 8 from GOG. It starts up and goes to character selection, then when I select "OK" for character, I get a "save file corrupted" message and more error codes on different lines each time I hit OK, until it eventually acts like it starts loading and stops halfway. I am running Windows 10. Have I wasted my money? Was really hoping to play this one.

No, because if they can't get it to work for you, support will give you a refund.

Is it installed in Program Files by any chance, if so try installing somewhere else.
Try setting different compatibility modes. A similar error for MM7 seemed to be fixed with Win 95 compatibility.

http://www.gog.com/forum/might_and_magic_series/save_game_corruption_in_mm7

Finally, contact support. Maybe they'll have a working suggestion.
http://www.gog.com/support/contact

Thankyou for your response. I found another post where someone had same problem for M&M 6 and 7 as well, where they turned off McAfee Real time scanning, which I also have running. When I turned it off, problem was fixed. It was installed in another location by the way. Also, I dabbled with compatibility settings on Windows 10, and I never did see where you could actually specify Win 95. Win 10 quizzed me on my problem, but it didn't seem to go back that far. I am sure it must be there somewhere. But I did not need to pursue that one for now. Thanks!