I spent the whole day playing this and I beat it late last night. Here's my list of the story changes:
Bespin is not in it, like at all.
The only planets you go to are Tatooine, Hoth, and Endor (You COULD count the Alderann meteor field I guess)
Episode IV is about the closest to the movies as you go from Tatooine to Aldarann, the Death Star, and finally the Death Star attack run
Episode V was condescend to Hoth. In this version the famous "I am your father" scene happens as they're evacuating Hoth, and Han never gets carbonited
Episode VI is condescend to Endor. The fight against Jabba and Bobba are totally omitted, so no Slave Leia for obvious reasons (Though you can visit the Sarlac pit in Tatooine. I'm EXTREMELY disappointed they didn't throw in a feat for playing as Bobba and throwing yourself into the Sarlac pit) I really wish we could have gotten Luke's green saber
I have to say though, I found that first part of the game trying to get the money on Tatooine to be extremely annoying and artificially time-consuming, but that's about my only gripe. (Well that and how annoyingly hard the Wampa Attack! mission is)
Overall I enjoyed it alot, even with the story changes.