For me, I need the change of temperature (sure it's between about 8 and 21-25C, but a variation). The lack of light in winter affects me more.
I've been through one Finnish winter and had visits to Tallinn (-30C), Stockholm (-12C) and Munich (0C) one work trip where 0c really felt like I should be wearing shorts.
What I can't deal with is hot and humid. Arrived in Germany about two weeks back, it was 33C and humid. Not enough showers would help not feeling "sweaty and dirty".
I think some variation is useful. I also miss rain.