I've always thought that Toddlers and Elders don't get enough interactions and new stuff but that's going off topic here. Back on topic, here's what I like about Seasons.
Spring: Great that Sims can do Easter Egg Hunts, the love type games seem funny as well, wildflowers, yes, another new collectable, not so happy about the allergies though, I get those in real life so don't want to see my Sims get them. Jumping in puddles is neat, can't wait to upgrade an umbrella, I wonder if we will get Japanese parasols? I hope so!
Summer: Return of the diving board! Rollerskating! Love the Snowcone machine. Fireworks, love the Sparklers. I really, really, really hope they release a stuff or store pack with the Surfing Stimulator and Beach Volleyball, some balls and water wings for the kids would be great too.
Autumn: Trick or Treating! Can't wait to try out the pumpkin carving and a Haunted House?! Awesome! Facepainting looks neat too. Hopefully Sims can jump in piles of leaves too and the Applebobbing, funny.
Winter: Snowboarding! Snowball fights look fun too, can't wait to see what kind of Snowmen and Igloos Sims can create. Iceskating looks like fun too. Not keen on my Sims getting sick or the Ice Lounge. Wonder if Skiing will be included.
I'm looking forward to this expansion in spite of the things they left out, hopefully those are planned for a stuff or store pack. I would personally love to see a Beach or Funpark themed pack myself.