From my experience working there- the vast majority of first timers are blown away and thoroughly impressed with and enjoy the parks. it's something they've thought about for a long time, budgeted for, planned for, researched because they were excited and had a blast with.
Magic Kingdom of course being the most "magical" as it's the "most Disney" of the parks for them. When they think Disney, that's the park they think of and the one they'll likely enjoy the most. but also really enjoying the other parks.
Right now I think they'll wonder what's going on at Epcot, especially with so much closed in Future World and no real focus there, but still enjoy it. Love seeing all the world pavilions, wish for more rides in the pavilions, and think that it's so huge and lots of walking.
Animal Kingdom just cool in so many ways. With Pandora it's finally hit a balance that it needed, though they may wonder why it doesn't have a parade. But they love the mix of rides, shows, animals, and Disney.
Studios- an obvious work in progress. While many of us miss the old studios, for a lot of the new comers steering it towards Pixar and Star Wars is a huge hit. I have a feeling for many that when SWGE opens that this park may rival MK for many first timers favorite park.
Now with all of that, there's the 10-25% of first timers that don't have a clue where they are, what they're doing, what's happening, or where the rides are. For the cast, they'll always be a source of both frustration and amusement that will likely never go away.