As of writing this review, I haven't used any expansion packs past this one, though I just got Free Time, so expect a review on that one in a couple of days.
That said, I think this is my second favorite pack after Nightlife. The actual changing of the seasons is fun, and the new things the sims can do depending on the weather are quite fun, though I haven't yet tried everything.
It wouldn't seem like an expansion pack revolving purely around weather could be that exciting, but it is. There are a few flaws, of course--the sims want to run to the windows every five minutes when there's new weather, just to check it out. But overall, the weather makes the world feel more cohesive. The winter interactions in particular are great fun.
Overall, one of the best expansion packs. I highly recommend it.