In terms of prices and range of games on sale?. Having experienced the Xmas sale last few years, it never feels like the prices are the best even though the gimmicks they use have either been good or people hate them.

Used to be the Christmas sale, especially back when almost everything was discounted by 50% - and that was still considered an awesome discount -, but these days every sale feels the same and the discounts mostly underwhelming, even if they're higher, because either the games were very expensive to begin with or the discounts hardly change anymore. I predict they will be more or less what you've seen in the Autumn sale, Summer sale etc. before. It's not just a GOG thing though, the same goes for most of the digital game stores.

The Imsomnia Sale was the best. Now it's just stuff on sale with mediocre discounts. Even full bundle discounts are very lackluster.
It kinda went downwards when Steam started to offer refunds. After that those hyper-low flash deals disappeared, and then they disappeared from the entire internet.