This what made my 1st trip to Universal Studios back in '94. Back then it was actually better then Disney-MGM in my point of view. We went to both Studios on our vacation. Universal Studios' hardly "Ride the Movies" now and at least MGM (now Hollywood) still has the feel as I went there last summer.
IOA's the reason USF's spared. NIck studios will be missed
If you really want to be slimed, stay at the Nick Hotel. They have a mass sliming at the pool everyday and I think you can schedule a special sliming through the hotel. Check their website for all the info.
The characters you see depends more on who licenses(TM) them, I think. If USF has a contract with the creators that allows them to use the characters, you'll see them. Universal doesn't create the characters, so they don't automatically hold the rights to the characters. I was hoping to see a bunch of Backyardigans characters and things, but they are probably privately licensed and someone else holds merchandising rights.