^ The X-Plane forums tend to get a load of complaints around the Christmas season, when they add a snow-fall effect that apparently kills usability and frame-rate on quite a number of users.
So it's not so much about how "big" or "small" the changes are, as much as how they effect the usability. If MLK's Halloween theme wasn't so... 1990s, then perhaps people wouldn't mind as much. I know I wouldn't. But because it is so different, and for some of us doesn't look that good, the reaction is understandable.
But hey, better than causing your computer to slow down to a constant 5 FPS, right?