This year marks my 3rd winter in Berlin.
When I moved I thought the worst would be the cold weather, but that's actually pretty manageable.
The small days are a pain, however (I had no idea about this "winter blues" thing).
It's kind of hard to explain, but I start to feel kind of tired and unmotivated when the days get shorter. I really need to leave the apartment a bit when there's still sun outside (even if the weather sucks).
It's also kind of bizarre how generalized this seems to be - You have a time of the year where people are gloomier than usual and just know that "it's normal, it's the winter".
FWIW, going to the office and to the gym has been helping quite a bit. If you are in a similar situation and have that option, I recommend trying it.
I do usually enjoy working from home, so this has the weird side effect that I actually go to the office more often in the winter when it's cold, raining and snowing than in the summer.