I'm very interested in the changes to vehicles and the models. I noticed that the Peacemaker went from being a cartoony Dodge Charger to a Nissan GTR sedan in the remaster. I think the Nelson got de-made back into a coupe as well.
edit: Looking at that remastered gameplay, I am downright impressed with a lot of the cars. The Taxi looks far more like a real Crown Victoria, the Justice looks great, the Genki car looks fantastic, and every other car I saw around looked far more like a real car than a lot of SR3's original vehicles did.