I think it's been a decade since I thought GLBC's beers were tolerable.
They also just straight up lie to you. "If you think our beers changed, it's your palate. We've never changed anything about our recipes" is absolute hogwash. Christmas Ale, in particular, the adjuncts have changed dramatically. I'm willing to guess that it's even the raw quantity--but if it isn't, then it's the quality and they're still making lies of omission. If you're using lower grade cinnamon that doesn't taste as cinnamony, and using the same amount, you changed the beer.
Also, all the beer brewers I know who know WAY more about this stuff than I do believe that Great Lakes has some weird interaction going on between their air and their malt which is causing that awful flavor.
It's sad--I used to enjoy Christmas Ale, and I'd put Dortmunder and Elliot Ness up there as great examples of their styles. Now, I'm embarrassed if someone from outside of Cleveland has to drink something from Great Lakes.
I still buy a pack of Christmas Ale every year though... foolishly holding out hope that maybe it's okay this year.