Due to family commitments I wasn't able to see The Avengers: Age of Ultron until Sunday night. These are my initial impressions and they may change over time, especially after multiple viewings. I am going to keep this post as spoiler-free as I can but I do have some plot point specific thoughts that I am going to put in another post.
Overall I give it a B+. The script was chock full of the witty banter that we have come to expect from the word processor of Joss Whedon and the general plot was well thought out. That said I can't shake the feeling that bits were missing. We know that there was a scene with Loki that hit the cutting room floor  and it seems there were several other small bits of dialogue that would have made various plot points clearer and they were excised in favor of action sequences. AoU clocks in at two hours, twenty minutes long so I'm not surprised things had to go. However if I may indulge in what I call the "Peter Jackson/Hobbit Rule of Action Films" if a film director needs to make a cut and it's a choice between 30 seconds of dialogue to advance the plot or 30 seconds of the good guys fighting be bad guys, cut the latter. It's an action film, we know and expect lots of fights and explosions but I'm willing to sacrifice an explosion for a bit of plot to help tie the whole thing together.
That said when it comes to those action sequences I do think Whedon is the present master of action choreography. Last week I noticed it again while watching the DVD of the first Avengers film and I saw it again last night watching AoU. Whedon gives a great deal of thought to what everybody and everything on the screen is doing. Not only are the moves of the characters well thought out if it's a one-on-one fight but also what everyone is doing in larger scale shots. Plus he things about the what happens to the various bits of collateral damage as cars and buildings go flying around. A superhero slugfest is essentially the same thing as a war with very similar effects on the bystanders and their surroundings and Joss takes this into account.
Getting back to the script, despite its occasional defects it still does a great deal towards getting into the heads and motivations of all the characters, making them more three dimensional people rather than the cardboard cut-outs that superheros tend to become on film. Especially noteworthy were the attempts by various Avengers to come to grips with Scarlet Witch screwing with their heads. Plus the conflicts between various characters seemed much more realistic in terms of each one's past and motivations rather than the rather simple optimistic, team-player Captain America versus cynical, loner Iron Man of the first film.
In conclusion, still a very good film. It could stand some improvements but I very much enjoyed it, plan on seeing it again and will own it when it's released on DVD.
 And this scene had better make its way into the DVD release, Mr. Whedon, or else we shall be having words.