Agreed 100%.
Cap was awful. Ultron was awful. Thor was wasted. Tony was blah. Natasha & Bruce's romance made no God damn sense. The twins were undercooked.
The only good characters were Vision & Hawkeye (and Serkis' small role as The Klaw).
I gave it a 7.5/10 when I left the theater. A year later its down to 7/10.
7/10 was RIDDICKs score for the first Avengers film if memory serves. I assume he'd go lower for AoU.