Oh! What about that scene where they finally reveal the baby, though? Right: For one thing, it's hard to even spot. If you've ever heard someone gush about the "baby scene" in that movie, allow me to shatter any perceptions of awesome you may have with this screenshot.
It's a Gremlin, basically.
Look, I get that they were working within the technological limitations of their day and that this was actually a neat idea back then and all of those other possible defenses of the movie. All fair points, but given all its modern-day shortcomings, why do people continue to recommend Rosemary's Baby as if it's some sort of essential watching in the "movies where the old people next door are Satanists" subgenre? This is a well that filmmakers have gone to time and again since then, often with much more entertaining results.
What You Should Watch Instead: The Devil's Advocate
It would be way too easy to suggest that you check out the 1976 masterpiece The Omen if movies about the biggest Red of all are your thing. In a perfect world, you've seen that movie like five times by now.
Watching it a sixth time certainly wouldn't kill you, but in the name of shaking things up, I'll take what I suspect might be a slightly controversial stance and say that, if you've never seen either movie, instead of watching Rosemary's Baby, give The Devil's Advocate a shot.