OK, relax. When we reach five expansion packs, I know there's part of you that just wants to set fire to EA for abusing those Sims-udders on the franchise-cow... but relax. The Sims isn't a game. It's a genre.
This is one of the lesser packs, adding nothing as standalone as the University pack, or new like the lustful Hot Date or the mercenary Open For Business, but still changing the world of The Sims on a daily basis. Literally, as this one's about the weather.
We progress from spring to summer to autumn to winter to... well, you know. In the standard Sims accelerated-world fashion, the seasons inch on every six days in the standard setup (the calendar can be altered, if you want to simulate global warming).
Snow is particularly well done, building to the point where you can have snowball fights. In more temperate months you can grow your own produce from seeds or fish from ponds - enabling you to create a true model of the Good Life if you can make a sufficiently cute Felicity Kendall Sim.
Away from the main thrust of the expansion pack, there's the usual selection of tweaks, including new careers. The most noticeable of which is "Gamer", which lends my own experience of Seasons a unique Pop-Will-Eat-Itself horror. There's plenty here to amuse passingly - the PlantPeople formed from Sims who overuse fertiliser are especially cute - but the lack of a core is testament to the lack of a real need for this expansion pack. That the main mechanistic change is the desperately-grasped-for and spurious concept that different seasons are optimal for different activities - spring for romance, etc - is further evidence.
All of which leaves this expansion pack as probably the least essential yet. It won't disappoint any fans, sure, but there's little to make lapsed devotees come in from the cold.
Weather or not, the forecast says: fans only. Best stay indoors.