The expansion packs sort of "specialize" in different themes and interests. They're all good, but my favorites are House Party, Hot Date, Unleashed and Makin' Magic. (I have all the expansion packs - I love my Sims!)
All expansion packs include new "skins" (clothing), new objects (furniture, lamps, electronics, etc) and new characters.
Here's some info on each expansion pack:
Livin' Large - "Luxury" items like marble statues, a pool table and a robot maid; a lovebed and some weird stuff like a genie and alien abduction. 5 new careers. More neighborhoods so you can have build up to different 50 homes/families. Themes for your home: Gothic Castle, "Love Shack" and high tech.
House Party - Everything you need to throw a killer party - DJ booth, caterer, dance cage, mechanical bull, dance floor. Western, luau and rave themes.
Hot Date - adds another neighborhood "downtown" where you can shop, have dinner, meet people, do the club scene ... you know, stuff you'd do on a date. New Sims interactions like cuddling, playing footsie and gossip. There's a cuddle couch, a romantic swing, a love tub and a picnic blanket with basket.
Vacation - Adds "Vacation Island" where you can go to the beach, a winter lodge, and camping. Volleyball, snowboarding, fishing, snowball fights, snow slide, and other fun stuff.
Unleashed - Pets for your Sims! Dogs, cats, fish, etc. New "Old Town" neighborhood has parks, cafes, shops and a market. Five new careers are added to the game. You can grow your own vegetables and sell them at the market for extra money.
Superstar - You can become a Rock Star, Movie Star or a Supermodel. "Studio Town" is a new neighborhood that has three themes: movies, music, and fashion. You can also hire a butler.
Makin' Magic - It's all about the supernatural. You can develop supernatural skills and cast spells, make potions, etc. "Magic Town" neighborhhod is sort of like a spooky carnival. There are rides and mini-golf. Lots of new items and characters with this pack.
The Sims Deluxe Edition - this includes The Sims (the original) and Livin' Large, as well as some new items that come exclusively with Deluxe.
The Sims Double Deluxe - includes The Sims (the original), Livin' Large and House Party
The Sims Mega Deluxe - includes The Sims (the original), Livin’ Large, House Party and Hot Date.
You can probably get more detailed info about each pack at Amazon.com.
FYI ... The Sims 2 comes out in September. The graphics are amazing! More info here:
http://thesims2.ea.comHave fun! :-)