I'm only going touch on Scarlet witch and Quicksilver quickly as there isn't much to go off on with them. Design wise, they both look good while still being faithful to the source material. I like the effect Quicksilver has when he's running but I'm not sure how it looks in the full movie as it has the potential to be a bit distracting to me. It'll be interesting to see how they play out in the movie itself as it looks like they could be on Ultron's side at one point in the film.
Quick note: Love the look of the Hulkbuster armor. I don't care how little we saw of it, it looks amazing. I just hope its gets a decent amount of screen time in Age of Ultron.
I can't talk about this without bringing it up, the Pinocchio music: I don't think its that bad. Considering what I know of Ultron (which is just basic searches, I'm not a avid Marvel or DC comics reader... in fact the only comics I read are the Sonic and Mega Man comics...) it does fit the character and while I do think it over emphasizes the point, especially with all the references to puppets including "there are no strings on me", I honestly didn't recognize the song until people started complaining about it (I haven't watched the film in over a decade).
Of course I'm going to say the movie looks great so far. I loved The Avengers and while I haven't seen Guardians of the Galaxy yet (YET, before people start yelling at me), I have herd good things about it. I'm interested in seeing how this goes, what the later trailers show off and what the final product is like. Expect a review of the movie next year.
On that matter though, something that you may or may not like, in the lead up to Age of Ultron's release in cinemas, I'll be doing another marathon like the Transformers Marathon covering all the Marvel movie verse films except for Guardians of the Galaxy along with Agents of S.H.I.E.L.D