I've posted my opinion of Sci-Fi before, but my general feeling is that things have improved significantly. Burgers and fries are fine, not outstanding, but the atmosphere can't be beat. And, my DD and friend split a penne pasta and shrimp entree that was amazingly good, better than my burger.
One little tip - if you decide to drop by on a whim without PS, they just about always have tables available, because most folks would prefer to sit in the cars. I remember our local drive-in having the same setup - picnic tables with umbrellas by the concession stand, and Sci-Fi has replecated that. You might lose a little of the charm by not sitting in the car, but the tables have the same view of all the goings-on.
Give it a shot. I'll give most any restaurant two chances to please me.