Good, certainly not great. Far behind some of the other Marvel movies but I still enjoyed it.
Far behind which other Marvel movies? GOTG, IM, and Winter Soldier are probably my top 3, but this and the first Avengers round out my top 5. Curious to know which ones you'd put so far ahead of this one?
You missed the emphasis on "some". I don't think our opinion is much different. I put Avengers, Guardians of the Galaxy and Iron Man 1 in my top 3. After that the list really starts to jumble together. There are parts of each MCU movie that I absolutely loved but collectively they don't stand out. I didn't like the Winter Soldier nearly as much as most (and I can't really put my finger on why) but that's not the same thing as me saying that I didn't like it - because I did and I've watched it at least 3 times already. So when I say far behind, all I'm really saying is that Ultron doesn't crack my top 3.
Sometimes I find that movies grow on me even more after second viewings... one of my favorite parts of all the MCU movies (and agents for Shield for that matter) is the "witty" dialogue and humor. Unfortunately with the exception of two scenes (IM/Hulk and Thor/Vision) I felt like I'd already seen all the "funny" stuff in the trailers. I suspect upon a second viewing, I won't have those same faults and will probably like it more.