I don't want to spoil anything, so I'll just make some general points:
- I would have thought that most people would know to stay until the end of the credits for Marvel movies, but I'd estimate a little more than half of the audience left early and missed the last scene. Having said that, significantly more people did stay for Iron Man 3 than I remember did for Iron Man.
- One thing I did fine puzzling was how the main villain died, at the end. Why did he die this time when he'd survived much worse?
- Given Robert Downey Jr.'s contract with Marvel has now expired, this may have been his last turn as Tony Stark. If this turns out to be true, I'll be disappointed, but also happy that Robert Downey Jr.'s run as Iron Man ended on such a high note.
- Assuming Robert Downey Jr. is done playing Tony Stark, I wonder which is more likely, that Marvel 'reboots' the character of Iron Man (like Batman and Spiderman), or that Marvel maintains continuity and simply replaces the actor. I'd lean towards the latter because of the way all the Marvel movies are linked together via The Avengers. Though right now I can't imagine anyone else in the role. For now, at least, Robert Downey Jr. = Tony Stark.