The Sims 2 Seasons Expansion Pack is a worthwhile addition to Sims 2 play. Seasons are six days long each, 4 seasons to a year, and are customizable (you can choose Spring, Summer, Summer, Fall, for example, and skip Winter). The seasons have unique activities (building snowmen, water balloon fights), and also affect other activities (Sims learn faster in Fall, for example).
The most significant addition to gameplay is gardening. Sims can have their own gardens, greenhouses, earn talent badges for their gardening, and can even turn into green PlantSims. PlantSims have different meters from Sims, they only require light, water, and love.
There are also lots of good, minor additions, such as the ability to fish in ponds, decorate pools, and add rinks (roller and ice skating) to community lots.