I am doing the original legacy challenge by Pinstar with scoring, so to get the points, it has forced me to try aspects of the game that I've never played before, which has been. The major one is Collecting. I still have yet to complete the feather collection from Cats & Dogs.
Other gameplay features I haven't explored:
Weather machine in Seasons
Having a Sim get struck by lightening
Tons of death types my Sims have not experienced (i.e. rabid rodent fever, poison, motherplant)
I've never played with a Sim with the glutton trait
I've never had a Sim with the grilled cheese aspiration
My Sims have never thrown a black and white party
