Well, yeah, there's plenty you missed!
For one, all of the Showtime achievments (You still get achievements, but not for Showtime).
We're also getting several Sims past favorites returning, such as the photo booth, the DJ, the Electrodance Sphere thingy, pool tables, the mechanical bull, jukeboxes, the golf course, and the karaoke machine.
As far as gameplay and other items go, you're also missing out on:
-The Genie, who not only can grant wishes, but if you add them to your family, he can magically conjure ANY food dish except Ambrosia. He can also magically clean stuff, I hear!
-All of the exclusive content from Simport that can be unlocked (which ALSO includes past favorites remodeled, such as the Freezer Bunny and the Social Bunny... I just realized how bunny-themed this EP is!)
There is also SO MANY things that you can get if you use SimPort! In fact, in my opinion, this EP isn't actually a full EP without the items that you can unlock!
-Your Sims can sing songs
-According to Black Garden I believe there is a vegetarian version of every dish currently available coming with this game
-Banana trees (Your Sims the bananas whole!

)
-Tofu
-Sing-a-grams for ANY occasion - happy, romantic, casual, and more!
-Special performance rewards
-Apparently, according to the chat, you can throw even a life preserver on stage if you're in the audience - ALSO, they seem to have created a system in The Sims where if you miss or hit another Sim while throwing something on stage, the object will bounce back at you!
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You can hire any of the performance careers for parties! (Or so I hear... from MULTIPLE sources that also went to one of the many demos in Europe!)
-Being able to see your friends' Sim actually come into your game, and perform on stage for you! You can also KILL your friends' Sims if they're a magician, apparently, too!
-The Simfest competition, with a person that actually comes out and introduces and sponsors the entire event!
-The Diva trait (This will make your town a lot more realistic, judging on real life behaviors. A lot of people act like this, believe it or not!)
-AWESOME, modern-looking, and for once,
highly realistic-looking rabbitholes!
-More combined rabbitholes, too!
-Performing for tips out on the street! Now you can literally create your own stories of a hobo living off of tips that they get from performing in the streets! This would be an AWESOME experience in Bridgeport, since in my mind, that's where most hobos would probably be found.
I'm sure there's lots more to it, also!
(If other people have posted this thread to a second page, I've been typing this for 3 hours... I've gotten sidetracked!)