This expansion is the best one EA's come out with. We've all been wanting it forever, and they listened very, very well.
As for the features...
Weather - snow, rain, heat, cold, hail, thunderstorms, etc. that we've been wanting for eternity.
Seasons - four seasons that you can rearrange and repeat any way you want. Each season has its benefits such as increasing skill rates or relationship boosts.
Objects - a "country" collection that old grannies might like. it seems like the whole EP was made for grannies, but you play awhile and it's certainly not the case.
Neighborhoods - no new sub-neighborhoods this time, but there is a new neighborhood called Riverblossom Hills with some nice pre-made lots and families
Activities - my favorite part! Introduced with Seasons is gardening, which takes up a lot of your Sims' time, but is worth it in the end, making the food from their fridge much more filling. The remnants of the more filling foods can be stored for later with the new LEFTOVERS feature. Fishing is another way to get great food. Both fishing and gardening have corresponding talent badges. In the winter when the ponds freeze over and your fruit trees go dormant, activities include snowmen, snow angels, snowball fights, ice skating ... and there are other activities such as playing catch or roller blading that are available outdoors in any season.
There's plenty more to discover, and I'm not even sure I've done it all yet! A word of advice: BUY THIS GAME.