We love Sci Fi, and we go every trip. While the theming is the main reason we go to Sci Fi, we also enjoy the food there. We always go for lunch (after one not-so-good visit at dinner) and stick to burgers (including the veggie burger), fries, onion rings, and shakes. All of these items have been very good every time we've been there. In our opinion, Sci Fi just isn't the kind of place where we'd order steak, salmon, or something like that. The overwhelming majority of reviews for these dishes at Sci Fi have been negative.
I finally tried 50's Prime Time for lunch last year with a friend. The theming was great, and we had a lot of fun, but I didn't think it was as fun as Sci Fi. I really expected to enjoy the food, but we didn't like it. I had the vegetarian stuffed peppers and my friend had the meatloaf. Both dishes were bland. My peppers were way too mushy, and the filling was greasy. My friend's meatloaf was dry.