In our experience, the atmosphere in both is terrific, but the food is not.
If visiting either of these eateries (both are immersive and fun -- go to 50's if you want to chat with your companions, and Sci-Fi if you'd prefer to take a break from socializing and watch some film clips in the dark), I suggest making a reservation late in the afternoon, long after you've eaten lunch, for the sole purpose of buying a milkshake or a light appetizer, and soaking up the ambiance.