I understand some people might be disappointed by the lack of actual footage in this, but give Disney a break. The movie doesn't come out for two years, and it's still knee-deep in pre-production. Honeslty, I think it's so much the better for not having random flashes of pointless footage or being an endless series of sweeping lens flares - we see Ultron people. Disney's just given us a good glimpse at Ultron. Granted, he looks exactly the same as he does in the comics, but it's nice to see the cinema interpretation of the world-killing android, especially two years ahead of the film's release.
Then, of course, we get to the question of Hank Pym. I've always seen him as an integral part of the Avengers line-up, and just as integral to Ultron's story. However, Whedon seems to have cut him out and made Tony Stark Ultron's creator instead. As painful as it is that they would change such a big piece of comic canon for the screen, I think this works very well; we've seen how crazy Stark is about his tech (remember that 'house party' in Iron Man 3?), so it's only the natural evolution of his story that he would one day create something that went wrong. Dangerously wrong. As in 'destroy the world' wrong. It would take too much time in the new movie to set up Hank Pym and Scarlet Witch and Quicksilver (who I am really excited to be seeing onscreen).
Finally, we get to the titles themselves. And the screams. Lots of screaming. Talk about setting the tone - Disney doesn't want us to forget that in many of the comic runs he appears in, Ultron kills anything from thousands to millions to, in his most recent run (also called Age of Ultron, though totally not worth a read) billions of puny humans. He's a furious killing machine that's more than a match not just for the Avengers, but for the whole world.
So now I'm really excited for The Avengers: Age of Ultron, and that's why. Not that I wasn't excited before, but now we have this teaser as proof of how awesome the movie is going to be. Joss knows what he's doing, and he's doing it right.