I saw this the other night and absolutely loved it. I'd give it a 9.6/10 easily. While there were some issues, no movie is ever going to be perfect compared to personal expectations. For a flick with so much going on, it was handled very well and is, IMO, every bit as good as, if not better than Avengers.
The representation of Vision was far and away much more than I'd have imagined they could pull off. Bettany was brilliant. Also, whereas there have been a lot of costume fails in recent movies, Vision's was electric. Stunning in every way.
I'm not a huge Hawkeye follower, so I'm not sure if it's in the comic book canon, but the reveal of his secret family just floored me. Never saw that coming, but it was really a cool twist.
The Veronica scene was over the top cool. Exactly the kind of Hulkbuster beatdown that we've all dreamt of. I could watch that bit on a continuous loop for hours. Wicked.
The only real letdown for me was Ultron himself. I felt that Spader was a lttle too flippant in his portrayal of what is undoubtedly the Avengers' most dangerous enemy. He was almost ... I'd have to say casual in his plotting the end of humanity. Nowhere near evil enough for me. Didn't really go for that. But what really bugged me about Ultron, and this is a purely technical complaint, was his mouth. A robot body, clearly constructed of metal, and yet he has soft, pliant, organic lips. WTF!?!?! Had the mouth been made of small bits that formed the shapes when he spoke, a la Transformers, I could have bought that, but the handling of the animation here just pulled me right out of the movie. Very poor technical choice by the director and animators.
My other continuing beef is with the ongoing Cap fail costume wise. There have been so many really badass costumes in the recent spate of CBMs, but Cap is always a letdown. The First Avenger was a good start and a great period costume, but was a bit unfinished in that he looked like a normal soldier in blue from the back. (no stripes or star) Since then, Cap's outfits have constantly missed the mark, IMO. In Avengers he look more like Captain Pajamas. The Winter Soldier gear was pretty cool, but not Cap and then they reverted to the FA costume. This one was no better in its incompletion. Captain America is the very definition of "wrapped in the flag" costuming. Why is it that everyone is so reluctant to detail the rear of this costume? The stripes (which just have to be stripes, not some weird squiggly red and white ergonomically designed whatevers) need to go all that way around the suit, and the star on his back is nearly as important. Otherwise, from the back, he's just a guy in a blue suit. It's like Batman without the bat or Superman without the "S". It just doesn't work.