-20 to -25C before windchill is relatively normal around here.
Below -25C requires a re-think on layering, masks, gloves, etc. but it can be comfortable with a bit of planning (more gondola, less chair, more sheltered runs, etc.) and usually less crowded.
For me though, below -35C isn't worth spending for lift tickets. If I'm already there, can't put it off until the next day and can't get a refund, then I'll do some runs, but otherwise....meh