We love Sci Fi. In 13 trips to WDW, its the one and only place we have been to each time. My kids love the place and I love the fact its quiet. I can just sit and enjoy my meal and the corny movie flicks. Its always pretty quiet in there, everyone old and young is riveted to the screen!
50's is another one we really like. However, if you have any members of your party who don't like to play antics with the servers, skip it. My kids do, but I have seen people who are clearly not enjoying the atmosphere and they always have thsi deer in the headlights look, fearing they are about to be called out! Not all servers get into the roll, and probably if you tell them to please back off a bit, they would. I just know not to take my inlaws there because I know they would hate that type of thing.
And if you go at dinner and want a burger don't despair, although burgers are not on the dinner menu, they always make one for me and I have heard many other people say the same thing. I love their burgers! And they are the same price as they are at lunch. No idea why they don't just include them on the dinner menu.