In summer the slab seems to absorb a lot of heat meaning our living room which has huge bi-folds, NW facing, never really overheats. And once the sun goes down and it starts cooling down outside, the slab starts releasing all the heat that has been stored during the day and it is lovely and warm inside.
I work from home and walk around in bare feet all year round. The concrete is a lovely warm temp in winter, and refreshingly cool in summer. Thermal mass is such an important consideration IMO. It can really make a huge difference to the comfort levels in your home. It basically acts as a big buffer, and is an excellent way to store heat when electricity is cheap in winter.
As already mentioned, insulation is also key to this. In particular slab-edge insulation, and not making any holes in your thermal envelope - i.e. downlights in the ceiling etc. Definitely worth spending a bit of time getting this right, it can make a huge difference to the enjoyment of living in your home IMO.