Pretty but not adding so much gameplay.
At first, you'll be amazed by the new graphics, but soon enough, you won't care. You'll even forget what season it is. And each "weather" is so short that it doesn't change much after all, especially if your Sims are inside.
Also, the actions linked with the seasons get pretty repetitive and often take priority over the aspirations of the Sims. So, in summer, EVERY Sim will want to play Marco Polo. In winter, everybody will want to have snowball fights, even if there isn't snow. Every fall, Sims will be obsessed by skills and in spring, by lovers... or gardening. You'll just end up making them fall in aspiration failures by ignoring their wants because you'll refuse to have clones all doing the same activites over and over.
About gardening. Seriously, I never saw plants that asked so much attention. And for what? Juice. Or sparkling food. Juice is... useless if you want my opinion. The efforts aren't worth the result. As for the sparkling food, it makes Sims fat! Sims who eat fresh food shouldn't be thinner than those who eat that pre-made food? They like it so much that they over-eat!
And plantsims are just boring. I usually love Sims creatures. Made a vampire-plant for some challenge and left it wandering under the sun... it didn't even die! They don't sleep, they don't eat, they are ugly... Can't go to the university either. And they are extremely long to make in the spraying way... No, plantsims are no good.
Now, the winter clothes. Cute at first, but once you realize that all your neighborhood is wearing the same coat... well, it gets pretty repetitive. By the way, ghosts wear winter coats... Weird!!!
Finally, some extreme deaths are coming a little too often. It is not rare to find somebody burnt in the hot tube, or frozen after having made a snow man. And children are a bit too easily taken by the social worker... for jumping on their beds. Seasons is definitely one of the less interesting expansion of the Sims 2. If you're a fan, you'll want it anyway, but it won't be the expansion that really changes your game, it will just add some graphics. That's it. For 45$.