Official description: Let your Sims swim in the ocean on a hot summer day, bob for apples in the autumn leaves, test their snowboarding skill on the half pipe, or welcome spring showers with a walk in the rain and a colorful umbrella. All-new activities, like soccer, and big seasonal festivals and celebrations bring the spirit of each season to life. Your Sims can pucker up at the kissing booth at the spring festival, or see what Halloween surprises await in the haunted house. Dress for the weather with seasonal fashions from sun dresses to raincoats and snow gear. With new foods, décor and weather effects, your Sims can enjoy the bounty and beauty of the ever-changing seasons and play with life like never before!
So, what do you think? Personally I didn't think it'd be possible for Seasons to exist for TS3 due to the high amount of power it'd need for the textures of rain and such. I'm guessing that this will still be resource heavy though, if TS2 is anything to go by. I'm sure that people will buy it regardless, as I know its been awaited eagerly by many fans.