In reply to C Rettiw:
I would say that on balance ours is no worse than any other tent I've had.
It has a large surface area, so absorbs quite a lot of heat. But it also ventilates well (we had two adults two children and a dog at -5°C and suffered no condensation), especially with the front open.
As long as you open up the front and the top vent it seems to shed the heat pretty efficiently.
I'll caveat this with the fact that we've never used it South of Cumbria, so there's a potential argument that we haven't encountered true sweatbox territory!