I’m surprised nobody’s mentioned I pagliacci. Leoncavallo’s music is a bit more complicated than Puccini’s, but it’s still quite accessible, and Pagliacci happens to be fairly short (some operas can suffer from length. Doesn’t bother me, but I wouldn’t subject a beginner to late Wagner). There’s also a Zefirelli movie with Domingo and Stratas available. I don’t love Stratas’s voice, but it’s still a pretty good presentation.
Speaking of Wagner, while I’d stay away from his later stuff, and, well his really early stuff, Der Fliegende Holländer (The Flying Dutchman) is quite melodic, and, remarkable for Wagner, not terribly long. Also features one of the creepiest opera choruses out there.
And, whatever you do, do not attempt Wozzeck.